Academic literature on the topic 'Tailing storage facilities'

The content of level has a big enough role in the value of the physical characteristic and the mechanical of material. The behavior of water in these materials needs to be analyzed first in order to support the slope stability analysis. Modeling of water behavior in materials in the construction of Tailing Storage Facilities (TSF) will be integrated in the slope stability analysis. This study aims to provide an explanation about the analysis of the Fishing Storage Facilities (TSF) which integrates transient groundwater analysis using the finite element method in supporting the stability analysis of the embankment of Tailing Storage Facilities (TSF). The variables that are used in the analysis, they are the parameters of physical properties and mechanic material for embankment and permeability parameters in analyzing groundwater. The analysis method for geotechnical and geohydrology modeling uses the finite element method. The results of analysis showed that groundwater behavior in the embankment material can be known in detail so that it can be integrated with stability analysis. It can be seen that there is a decrease in the value of the slope safety factor using the Integrated Slope Stability Analysis method compared to the conventional method. Adding an impermeable layer using a thickness of 5 m of clay material and a thickness of 20-30 m to support the retaining wall/foot is the criterion of optimal stability. The required lining material thickness (D) can be expressed by the following drawdown percentage equation function: reduction percentage = (1-0.8661D (-0.031)) * 100%.

A lot of drilling wastes with various content of oil products is formed annually during production of hydrocarbons in the result of accidents at the facilities of transportation and oil production, soil is polluted. So, main contaminants of the environment are drilling wastes such as drilling, drilling waste water, waste drilling fluid and places of their disposition - sludge pits. Total amount of the oil slurry annually formed at enterprises of the oil sector of Kazakhstan is about 100 thousand ton, and resources of these wastes are estimated in more than 40 mln. ton. The wastes are placed in special sludge pits equipped with watertight screen. However, in spite of the available modern technologies for arrangement of waterproof finish of the drilling waste disposal facilities, high level of soil pollution is still observed. As a rule, pollutions are related to violation of the requirements of the standards during construction and operation of sludge pits, products pipelines, tailing dumps, sludge collectors and temporary storages. Therefore it is necessary to build reliable storages for temporary placement of the formed wastes until their delivery for recovery or disposing, during operation of which there will be no migration of pollutants to the environment. It is suggested to use bentonitic mats as waterproof finish of such facilities - this is innovative by properties, multifunctional composite material, which is combination of textile materials with the layer of the natural self- recovering mineral component - bentonite.

Aeolian dispersal of dust from gold mine tailing storage facilities impacts negatively on amenities, human health, and the environment of the Witwatersrand region, South Africa. The present study adopted a multivariate analytical method to quantify the effect of specific meteorological parameters on dust fall emissions, monitored at 22 sites in the central Witwatersrand area. Using meteorological and dust fall data from 2001 to 2010, the relationships between weather and dust fallout deposition rates were explored across the sites at different seasons. Dust deposition rate varied among seasons, with spring months showing the highest levels and frequency. Atmospheric humidity had negative correlations () with dust fall while wind speed showed positive correlations () at the selected sites (). Sites with low influence of relative humidity had higher impact on wind speed. Mean relative humidity below 50% and mean wind speed above 4 m/s were predicted as critical levels for dust episodes incidence at sites that recorded “heavy” and “very heavy” dust fall. For environmental planning purposes, current mitigation measures should be manipulated in relation to levels of air humidity and wind speed for dust emission reduction, especially during spring.

The article deals with the issues of the emergence of a new stressed state of rocks during the development of deposits and the formation of several deformations of the sides of the quarries. It is noted that among which gravitational slope deformations in the form of landslides, talus and mudslides are of decisive importance. All these types of deformation are observed in the Sary-Cheku, Kalmakyr, Kurgashinkan and others deposits. As a result of the analysis of the deformation of the quarry walls, the main conclusions were made, which can serve as a basis for the study and forecasting of landslide and other types of deformations. The issues of the technogenic (anthropogenic) impact of industrial enterprises and quarries of the Almalyk region on the environment are also considered. As a result of the infiltration of polluted waters of quarries, dumps, slag ponds and tailing dumps of factories, there is a penetration of polluting components into underground groundwater. Under the influence of the infiltration flow, the chemical composition of soils changes, and several polluting chemical compounds accumulate on their solid particles. Surface wastewater associated with the washing out of sludge and slag from industrial waste storage facilities is also susceptible to pollution.

In the article, a new method is presented for calculating hydraulic slope and critical speed of cleaning reject hydrotransportation through the polyethylene pipelines, which is based on the Methodology for Calculating Hydrotransport Plants for Tailings Transporting and Inwashing at the Iron Ore Mining and Processing Enterprises. This methodology was approved by the State Construction Committee of the Ukrainian SSR in its Temporary Instructions on Technology of the Tailing Dump Arrangement and was used in the design of all of the waste storage facilities in the Krivyy Rih ore-dressing and processing enterprises. For the conditions of the experiments, it was shown that experimental multiplier in the formula for calculating critical speed of hydrotransportation was depended on the pipeline diameter, free fall acceleration, kinematic coefficient of water viscosity and absolute roughness of the pipe inner surface. The acknowledgement of these factors made an empirical constant in the considered formula dimensionless and close to average value of the constants in the formulas obtained by other similar methods. With the considered method, it is proved that experimental constant in the formula for calculating critical speed of hydrotransportation is inversely proportional to the cubic root of the roughness of the pipeline inner surface, while coefficient of proportionality is a universal constant, which does not depend on the properties of the pipeline material and is equal to 10.1. Therefore, for determining critical speed of hydrotransportation through the polymer pipes by using this method, it is necessary to multiply critical speed for steel pipe with a similar diameter by the cubic root of ratio of roughness of the inner surfaces of the steel and polymer pipelines. It is further shown that value of hydraulic slope significantly depends on the operating coefficient, which shows by how many times coefficient of friction hydraulic resistance in the polyethylene pipe operating in supercritical flow regime exceeds the same value in case of critical flow regime for the same pipe. The research results allowed finding formulas for calculating hydraulic slope and critical speed of the iron-ore cleaning reject hydrotransportation through the polyethylene pipelines, which are based on the dependencies obtained for the steel pipes and value of absolute roughness of the pipeline inner surface.

The global mining community has seen a dangerous sequence of failures in tailings dams, beginning with Mount Polley mine, followed by the Samarco, Cadia Valley and Córrego do Feijão mines. This sequence of failures began on August 4, 2014, at the Mount Polley tailings storage facility in British Columbia, Canada. The initial failure in the embankment at the Mount Polley tailings storage facility had substantial impact on the global mining industry. The Independent Expert Engineering Investigation and Review Panel (IEEIRP) tasked with the investigation of the breach in the tailings dam at Mount Polley made major contributions for new guidelines. The incident has given rise to comprehensive recommendations for best available tailings technologies (BAT) based on principles such as the elimination of surface water from impoundments with the promotion of unsaturated conditions in the tailings through drainage provisions. The application of these BAT principles for the surface storage of tailings leads to the use of filtered tailings technology. Filtered tailings technology or “dry stack tailings” can satisfy each of the BAT components when the impoundment is properly designed and constructed. The implementation of the best available technologies for the physical stability (BAT-PS) of tailings impoundments competes directly with the best available technologies for the chemical stability (BAT-CS) of reactive tailings that may produce acid and metalliferous drainage. The new expertise in mine waste management required to achieve both BAT-PS and BAT-CS are discussed in the present paper.

Tailings storage facilities (TSFs) and conventional water retaining dams are the largest manmade structures on Earth. Statistics show that TSFs are more likely to fail than water retaining dams.Recent catastrophic failures of TSFs have led to the loss of lives (Germano mine, Brazil), environmental damage (Mount Polley, Canada), contamination of drinking water (Baia Mare, Romania), and the destruction of property (Kingston Fossil Plant, USA). As the scale of mining increases, TSFs increase in height and volume, therefore increasing the consequence of failure. To help mitigate risk associated with large TSFs mining companies empanel expert groups to review operations of TSFs and conduct regular visual inspections. In the US the Mine Safety and Health Administration has regulatory responsibility for the safety of TSFs. As population centers expand nearer to existing and proposed TSFs, the public requires assurance of the integrity of these structures. A pro-active approach to public safety is more desirable than a post-mortem analysis after a major failure. We have examined both the regulatory practices, the industry practices, and public data on TSFs in Arizona. In this thesis paper we address inadequacies of the official government records on TSFs in the two largest publicly accessible databases of dams inthe US – the National Inventory of Dams (NID), and the National Performance of Dams Program (NPDP). Both databases contain numerous errors and omissions, including descriptions and geographic coordinates of TSFs that are inaccurate by many kilometers. Several large TSFs in Arizona are not included in either database.We address these shortcomings with a pilot project for Arizona that demonstrates recording accurate information in a database is neither expensive nor onerous, communicating best practices for operation can help alleviate community concerns, and continuous monitoring technology can resolve shortcomings with visual inspections.

South Africa is one of the most important mining countries in the world, hosting the world's largest reserves of platinum group metals (PGMs). Even though mining is clearly an important activity in South Africa, contributing approximately US$ 7.4 billion annually to the countries' gross domestic product (GDP), the costs to the environment are not insignificant. One of the most severe environmental aspects associated with mining is the storage of mineral waste on tailings storage facilities due to their impacts on air quality, ground water quality, aesthetics and land use. It is also unknown whether the environmental effects of tailings storage facilities increase or decrease over time. The aim of this study was to determine the ecotoxicity of platinum tailings storage facilities of different ages by means of soil physical and chemical analysis, earthworm ecotoxicological studies, dehydrogenase activity and soil mesofauna studies. Samples were obtained from three platinum tailings storage facilities of different ages of which two were already rehabilitated while the third was still operational at the time this study was performed. The latter was used as a negative control for the purpose of the study. Soil samples were physically and chemically analysed. Earthworm ecotoxicological studies were conducted to determine changes in biomass, reproduction, mortality, neutral red retention times and tissue metal concentrations. Dehydrogenase activity was determined before the introduction of earthworms and manure, after introductions of manure and after introductions of earthworms and manure. Soil mesofauna were extracted and identified in order to determine species richness, diversity, abundance and functional grouping. Soil chemical analysis indicated that concentrations of certain heavy metals, especially chrome (Cr), present in platinum tailings materials could have a potential effect on microorganisms, microbial processes and earthworms. Earthworm ecotoxicological results indicated that earthworms that bioaccumulated higher levels of heavy metals showed poor hatchability of cocoons. Dehydrogenase activity indicated that earthworms play a significant role in increasing the number and biomass of soil microbes because significant increases in dehydrogenase activity were noticed after the addition of earthworms to platinum tailings materials. Results from the earthworm ecotoxicological studies, dehydrogenase activity, and soil mesofauna composition indicated that environmental impacts of tailings storage facilities did not increase with age, but is more likely to be an indication of the rehabilitation measures administered to the different tailings storage facilities.
Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2009.

Tailings facilities are vast man-made structures designed and built for the storage and management of mill effluents throughout the life of a mining project. There are different types of tailings storage facilities (TSF) classified in accordance with the method of construction of the embankment and the mechanical properties of the tailings to be stored. The composition of tailings is determined by the mineral processing technique used to obtain the concentrate as well as the physical and chemical properties of the ore body. As a common denominator, TSFs are vulnerable to failure due to design or operational deficiencies, site-specific features, or due to random variables such as material properties, seismic events or unusual precipitation. As a result, long-term risk based stability assessment of mine wastes storage facilities is necessary.The stability analyses of TSFs are traditionally conducted using the Limit Equilibrium Method (LEM). However, it has been demonstrated that relying exclusively on this approach may not warrant full understanding of the behaviour of the TSF because the LEM neglects the stress-deformation constitutive relationships that ensure displacement compatibility. Furthermore, the intrinsic variability of tailings properties is not taken into account either because it is basically a deterministic method. In order to overcome these limitations of the LEM, new methods and techniques have been proposed for slope stability assessment. The Strength Reduction Technique (SRT) based on the Finite Element Method (FEM), for instance, has been successfully applied for this purpose. Likewise, stability assessment with the probabilistic approach has gained more and more popularity in mining engineering because it offers a comprehensive and more realistic estimation of TSFs performance. In the light of the advances in numerical modelling and geotechnical engineering applied to the mining industry, this thesis presents a stability analysis comparison between an upstream tailings storage facility (UTSF), and a water retention tailings dam (WRTD). First, the effect of embankment/tailings height increase on the overall stability is evaluated under static and pseudo-static states. Second, the effect of the phreatic surface location in the UTSF, and the embankment to core permeability ratio in the WRTD are investigated. The analyses are conducted using rigorous and simplified LEMs and the FEM - SRT. In order to take into consideration the effect of the intrinsic variability of tailings properties on stability, parametric analyses are conducted to identify the critical random variables of each TSF. Finally, the Monte Carlo Simulation (MCS), and the Point Estimate Method (PEM) are applied to recalculate the FOS and to estimate the probability of failure and reliability indices of each analysis. The results are compared against the minimum static and pseudo-static stability requirements and design guidelines applicable to mining operations in the Province of Quebec, Canada.Keywords: Tailings storage facilities (TSF), Limit Equilibrium Method (LEM), Shear Reduction Technique (SST), pseudo-static seismic coefficient, probability of failure, Point Estimate Method (PEM), Reliability Index.
Les parcs à résidus miniers (PRMs) sont de vastes structures utilisées pour le stockage et la gestion des déchets pendant l'opération et après la clôture d'un site minier. Différentes techniques d'entreposage existent, dépendant principalement de la méthode de construction de la digue et des propriétés physiques, chimiques et mécaniques des résidus à stocker. La composition des résidus est déterminée par la technique utilisée pour extraire le minerai du gisement ainsi que par les propriétés physico-chimiques du gisement. De manière générale, les installations de stockage de résidus miniers sont dans une certaine mesure, sujettes à des ruptures. Celles-ci sont associées à des défauts de conception et d'exploitation, des conditions spécifiques au site, des facteurs environnementaux, ainsi que des variables aléatoires telles que les propriétés des matériaux, les événements sismiques, ou les précipitations inhabituelles. Par conséquent, la stabilité des PRMs à long terme est nécessaire sur la base de l'évaluation de risques.Les analyses de stabilité sont généralement effectuées à l'aide de la méthode d'équilibre limite (MEL), cependant, il a été prouvé que s'appuyer exclusivement sur les MELs n'est pas exact car la relation entre déformation et contrainte est négligée dans cette approche, tout comme le déplacement ayant lieu au pendant la construction et l'opération des PRMs. En outre, la variabilité spatiale intrinsèque des propriétés des résidus et autres matériaux utilisés pour la construction des PRMs n'est pas prise en compte. En conséquence, de nouvelles méthodes et techniques ont été développées pour surmonter les limites de la MEL. La méthode des éléments finis (MEF) et la Technique de réduction de cisaillement (TRC), par exemple, ont été appliquées avec succès pour l'analyse de la stabilité des PRMs. De même, l'approche probabiliste pour l'analyse de la stabilité des pentes a gagné en popularité car elle offre une simulation complète et plus réaliste de la performance des PRMs.À la lumière des progrès réalisés dans le domaine de la modélisation numérique et de la géotechnique pour l'industrie minière, cette thèse présente une comparaison entre une installation d'entreposage des résidus en amont et un barrage de stériles et d'eaux de décantation.En premier lieu, l'effet de l'augmentation de la hauteur des résidus sur la stabilité globale est évalué en vertu des états statiques et pseudo-statiques. En deuxième lieu, l'effet de l'emplacement de la nappe phréatique dans installation d'entreposage des résidus en amont et le rapport de perméabilité de remblai dans le barrage de stériles et d'eaux de décantation sont étudiés. Les analyses sont conduites en utilisant la modélisation numérique des MELs et la MEF – TRC.Des analyses paramétriques sont effectuées pour identifier les variables aléatoires critiques de chaque parc à résidus miniers. Finalement, pour évaluer, la simulation de Monte Carlo (MCS) et la méthode d'estimation ponctuelle (MEP) sont appliquées pour recalculer les facteurs de stabilité et pour estimer la probabilité de défaillance et les indices de fiabilité qui leur sont associées. Les résultats de chaque analyse sont comparés aux exigences minimales de stabilité des pentes applicables aux opérations minières dans la province de Québec, Canada.Mots-clés: Parcs à résidus miniers (PRMs), coefficient sismique, Technique de Réduction de Cisaillement (TRC), probabilité de défaillance, Méthode d'Estimation Ponctuelle (MEP), indice de fiabilité.

Magister Scientiae - MSc (Earth Science)
The city of Randfontein, in the Witwatersrand, hosts several slimes and tailings storage facilities which pose potential threat to the environment in the form of acid mine drainage (AMD). The latter, readily scavenges toxic metals, contaminating surrounding soils and water resources, thereby potentially compromising the overall environmental- and public health of the area. To this end, three slimes sections (section T001, T002 and T003) from the Gold One Millsite Slimes Complex were investigated, with the aim of understanding metal release from the slimes dam into the Randfontein area. To achieve this, the mineralogical and geochemical factors controlling metal release were investigated using combined core log analysis, cluster and discriminant analysis, x-ray diffraction analysis, bulk geochemical analysis, acid base accounting methods and selective sequential extraction procedures.

Gold mining generates large quantities of tailings waste. These tailings can have a significant negative impact on the surrounding environment, with concomitant effects on local ecosystems, as well as on human health and quality of livelihoods. The latter is a concern in the Witwatersrand goldfields of South Africa, where communities are located in close proximity to gold mining operations and/or both current and defunct tailings dumps. This research project was, therefore, aimed at developing a better understanding of the facts, perceptions, concerns, and expectations associated with Witwatersrand gold mine tailings storage facilities, and how these are related. In order to fulfil this aim, a desktop study was conducted which involved a detailed review of published academic literature, company reports, newspaper articles, gold mining magazines, and specialist reports with specific emphasis placed on the Central Rand goldfields of the Witwatersrand Basin. Semi-structured interviews were also conducted with representatives from the community, civil society organisations and independent experts, using the defunct Princess gold tailings dump in Davidsonville Suburb (West of Johannesburg) as a case study. The literature review of the study has shown that there is environmental pollution (air, water and soil) due to gold tailings dumps in current and historic gold mining areas. These findings were found to be largely consistent with perceptions and concerns of the community members, civil society organisations and subject matter experts. The long-term impacts of this pollution are not only environmental but cause a huge social burden on health and quality of livelihoods. Not only is dust considered a nuisance, particularly in the windy season, but the dust has been proven to contain crystalline silica and radionuclides. The long-term exposure to this dust can lead to skin problems and respiratory illnesses. There is higher exposure of ambient particulate matter (PM10) in areas around tailings even at distances up to 2 km downwind from the tailings dumps. Acid mine drainage, on the other hand, increases metal load in watercourses and soils, ultimately affecting the ecosystems as the metals are toxic to plants. Metal contamination has adverse impacts on animal and human health. In addition to literature survey, results from the semi-structured interviews revealed that there are conflicts between the communities, government and mining companies, with communities associating their health problems with gold mine tailings. This has led to court cases and gained media attention. The complex relationships between mine waste, the environment, and community health and livelihoods are still not well understood, making it difficult to justify and motivate the implementation of meaningful interventions to mitigate risks associated with gold tailings dumps. To date, little attempt appears to have been made to support community concerns and perceptions with factual evidence and information. Overall, this study has demonstrated the existence of longstanding issues associated with defunct gold tailings dumps and the communication gab that existing between various stakeholders, i.e. community, government and mining houses. These emphases the importance of having adequate remedial actions to prevent further pollution, the need to engage all relevant stakeholders when dealing with gold tailings and implementation of regulatory frameworks associated with gold tailings reclamation and rehabilitation.

As a result of the mining that has taken place over the last century in South Africa, many towns and cities have developed around mining hubs, the most significant of these being the city of Johannesburg. Over the years, residential areas have grown around these mine sites, even well after decommissioning of the mining activities. The mining activities left a lasting legacy of derelict mining infrastructure with negative effects on the surrounding environment and community, such as dormant mine shafts, sterilised land and abandoned Tailings Storage Facilities (TSFs). Due to lack of funds, commitment from mine owners and regulators these facilities are often left unrehabilitated, posing negative environmental impacts, including potential health hazards to the surrounding community. This legacy of problems posed by abandoned mines encountered in South Africa is probably unique in scale compared to any country in the world. A significant problem South Africa currently faces is an electricity shortage, especially during the high demand season from the start of June to end of August, when it is winter in South Africa. This period is occasionally associated with so called controlled “load shedding”, i.e. managed power interruptions to prevent overload and subsequent collapse of the electricity supply and distribution network. South Africa is highly reliant on coal-fired power stations for the majority of electricity consumed, which has detrimental effects on the environment due to high carbon emissions. However, a global shift towards renewable energy, as well as South Africa’s energy shortage, has forced the National Energy Regulator of South Africa to encourage greener alternatives. This study is aimed at finding an opportunity to generate more electricity, which is sustainable and with reduced carbon emissions. This study was conducted to determine the financial and practical feasibility of generating energy from the ERGO TSF, near Brakpan Johannesburg, as a post closure land use option. The following options were investigated: • Solar Photovoltaic electricity generation • Pump storage scheme development • A combinations of the above In addition, rainwater harvesting and wind power generation were also considered, but were abandoned early on in the study. From the study it was concluded that a Solar PV plant on top of the ERGO TSF will achieve the highest possible IRR of 10.70% and a power generation capacity of 471.9 MWp. Developing a pump storage scheme at the ERGO TSF can achieve an IRR of 10.27% and generation capacity of 78.2 MW. Combining the two options independently on the same site will result in an IRR of 10.61% and a combined peak generation capacity of 550 MW. If the combined system is required to be independent of the surplus electricity available in the grid an IRR of 10.32% and a combined generation capacity of 550 MW is achievable. From a financial and technical perspective it is considered to be most beneficial to implement only the solar PV plant on top of the ERGO TSF. Construction of a pump storage scheme on TSF is considered to be a challenging undertaking and seeing that its generation capacity is only 17% of that of the solar PV facility on the same ERGO site, it is probably not the optimal solution for utilisation. Solar panels are light weight structures that can easily be installed in large numbers on TSFs with little engineering challenges.
Dissertation (MEng)--University of Pretoria, 2015.
tm2015
Civil Engineering
MEng
Unrestricted

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, 2016
The performance in tailings storage facilities (TSFs) of three methods based on the cone penetration test (CPT) to assess liquefaction potential is explored. For two of these methods the investigation highlights potential limitations mostly related with the experimental data that supports some of the equations used by the methods. However, the methodologies yielded mostly correct performance predictions when implemented on TSF case histories in which an undrained response is believed to have occurred. The positive performance of both methodologies must be tempered by the limitations identified in the methods. The steady state line (SSL) is an input of the third method considered. Accordingly, the correlation between the SSL and soil index parameters was investigated using a database of 151 non-plastic soiltypes compiled from data previously reported in the literature. The SSLs were modelled in void ratio (e) - mean effective stress (p') space, using a logarithmic equation. The y-intercept of the SSL is termed Γ, and the slope is termed λ. A direct, and linear (R2 = 0.74) correlation between the minimum void ratio (emin) and Γ was found. Although previous research has explored the effect of non-plastic fines on the SSL, the analysis presented herein shows that the Γ-emin correlation is independent of fines content. The correlation is also independent of the angularity of the particles provided that these are bulky, as opposed to platy. A direct λ-emin correlation was also found; however this correlation is much weaker and probably obscured by uncertainties in void ratio measurements. Triaxial testing was conducted to determine the SSLs of three tailings soiltypes obtained from a single TSF. The trends observed in the resulting SSLs are in agreement with the Γ-emin and λ-emin correlations from the database. An assessment was made of the sensitivity of the third method, which is based on a state parameter (ψ), to variations in λ throughout a single TSF. It was found that in some TSFs, the variations of λ are small enough to be disregarded without significantly affecting the accuracy of ψ. However, in other TSFs it is necessary to estimate how λ varies throughout the deposit. iii
CK2017

Ph.D., Faculty of Science, University of the Witwatersrand, 2011
Deep-level gold mining in the Witwatersrand Basin Goldfields (WBG) of central South Africa is characterised by the production of extensive unlined tailings storage facilities (TSFs) comprising large quantities of pulverised rock and water contaminated with salts and a wide range of other inorganic pollutants (Weiersbye et al., 2006). There are more than 200 such TSFs covering a total area of more than 400 km2 (Rosner et al., 2001), and significant contaminated “footprint” areas occur after removal and reprocessing of the original TSFs (Chevrel et al., 2003). It is estimated that the Witwatersrand Basin contains six billion tons of gold and uranium tailings (Chevrel et al., 2003), 430 000 tons of uranium (Council of Geoscience, 1998; Winde, 2004a; b; c) and approximately 30 million tons of sulphur (Witkowski and Weiersbye, 1998a). An estimated 105 million tons of waste per annum is generated by the gold mining industry within the WBG (Department of Tourism, Economic and Environmental Affairs, 2002; Chamber of Mines of South Africa, 2004). A major environmental problem resulting from deep level mining in the WBG is the contaminated water that seeps from TSFs into adjacent lands and groundwater. Van As (1992) reported on the significant environmental hazards resulting from the storage of highly pulverised pyrite rock waste in TSFs (Straker et al., 2007). Adjacent lands become polluted through near-surface seepage, and this is enhanced by the movement of polluted groundwater in shallow aquifers that are commonly 1-30 m below ground (Funke, 1990; Hodgson et al., 2001; Rosner et al., 2001; Naicker et al., 2003). The impact of the mines and the TSFs extends far beyond their localities (Cogho et al., 1990). The Vaal River catchment receives a large proportion of the pollutants from WBG mining activities, with consequent acidification and salinisation of surface and ground waters. Salt discharges to the Vaal River were estimated to be 170 000 t/annum (Best, 1985), whereas discharges from the Free State gold mines south of the Vaal catchment were estimated at 350 000 t/annum of salts (Cogho et al., 1990). Concern also exists over the spread of dangerous contaminants such as uranium, chromium and mercury (Coetzee et al., 2006; Winde, 2009). Engineering solutions to these problems are hindered by the large sizes and great extent of TSFs, the high and indefinite costs involved, and the typically low hydraulic conductivity in affected aquifers, which makes the “pump and treat” option impractical. An alternative phytoremediation strategy is to establish belts or blocks of trees in strategic areas surrounding the TSFs in order to reduce the seepage of contaminated water into adjacent lands and groundwater bodies. The major reasons why trees are likely to have a greater impact on seepage water than the existing grasslands that characterise the area around most TSFs in the WBG, are that some tree species have the potential to develop very deep root systems and to continue transpiring water throughout the year. This is in contrast to seasonally dormant grasslands. In addition, some tree species are known to be tolerant to salts and other pollutants. Trees are thus potentially able to reach deep water tables, take up large quantities of water, and remove some of the pollutants in this water. It is crucial for a successful implementation of this strategy to know on what sites trees are able to access mine seepage water, and consequently maintain a high year-round rate of water use. If this access is limited, then growth and water use will be curtailed during the long winter dry season, and control of seepage will be considerably below potential. A primary aim of this study was to develop methodologies to discriminate between water-stressed and non-water-stressed trees currently growing in three gold mining districts (Welkom, Vaal River, West Wits) within the WBG. This information was required to assess what site types are likely to support adequate tree growth and permit high rates of water use and seepage control. The tree species selected were those most widely occurring in these areas, and include the non-native species Eucalyptus sideroxylon A. Cunningham ex Woolls and Eucalyptus camaldulensis Dehnhardt, as well as the indigenous species Searsia lancea L.f. Various remote sensing technologies including leaf-level spectroscopy, satellite and airborne remote sensing images were evaluated for their usefulness in detecting levels of winter-time water stress. Four commonly used ground-truthing techniques (predawn leaf water potential, leaf chlorophyll fluorescence, leaf chlorophyll and carotenoid pigment content, and leaf water content) were used for localised measurements of plant water stress and for ground-truthing of remotely sensed data on 75 sample sites and 15 sample sites. This study provided a unique opportunity to test and compare the use of stress reflectance models derived from different remote sensing data acquired at different spatial and spectral resolutions (i.e. multispectral and hyperspectral) for the same geographical location. The use of remote sensing to examine the spectral responses of vegetation to plant stress has been widely described in the scientific literature. A collation of published spectral reflectance indices provided the basis for investigating the use of hand-held remote sensing technology to detect plant water stress, and was used as a stepping stone to further develop spectral plant water stress relationships for specific tree species in this study. Seventy seven spectral reflectance indices and specific individual spectral wavelengths useful for detecting plant water stress, plant pigment content, the presence of stress related pigments in vegetation, and changes in leaf cellular structure, were investigated using hand-held spectroscopy. Ground-based measurements of plant water stress were taken on 75 sample trees. In this study, the measurement of predawn leaf water potential has been identified as a key methodology for linking remotely sensed assessments of plant water stress to actual plant water stress; a reading of -0.8 MPa was used to separate stressed trees from unstressed trees in the landscape (Cleary and Zaerr, 1984). The results of the predawn leaf water potential measurements ranged from -0.56 to -0.68 MPa at unstressed sites, and from -0.93 to -1.78 MPa at stressed sites. A novel approach of using spectral reflectance indices derived from previous studies was used to identify specific indices which are applicable to South Africa and to the three species investigated in the WGB. Maximal multiple linear regression models were derived for all possible combinations of plant water stress measurements and the 77 spectral reflectance indices extracted from leaf-level spectral reflectance data, and included the interactions of district and species. The results of the multiple linear regression models indicated that the (695/690) index, DATT index (850-710)/(850-680), near infra-red index (710/760) and the water band (900/970) index performed well and accounted for more than 50% of the variance in the data. The stepwise regression model derived between chlorophyll b content and the DATT index was selected as the “best” model, having the highest adjusted R2 of 69.3%. This was shown to be the most robust model in this application, which could be used at different locations for different species to predict chlorophyll content at the leaf-level. Satellite earth observation data were acquired from two data sources for this investigation; the Hyperion hyperspectral sensor (United States Geological Survey Earth Resources Observation Systems) and the Proba Chris pseudo-hyperspectral sensor (European Space Agency). The Hyperion sensor was selected to obtain high spatial and spectral resolution data, whereas the Proba Chris sensor provided high spatial and medium spectral resolution earth observation data. Twelve vegetation indices designed to capture changes in canopy water status, plant pigment content and changes in plant cellular structure, were selected and derived from the satellite remote sensing imagery. Ground-based measurements of plant water stress undertaken during late July 2004 were used for ground-truthing the Hyperion image, while measurements undertaken during July 2005 and August 2005 were used for ground-truthing the Proba Chris images. Predawn leaf water potential measurements undertaken for the three species, ranged from -0.42 to -0.78 MPa at unstressed sites, and -0.95 to -4.66 MPa at stressed sites. Predawn leaf water potentials measured for E. camaldulensis trees sampled in species trials in Vaal River were significantly different between stressed and non stressed trees (t = 3.39, 8df, P = 0.009). In contrast, E. camaldulensis trees sampled near a pan within the Welkom mining district, which had greater access to water but were exposed to higher concentrations of salts and inorganic contaminants, displayed differences in total chlorophyll content (t = -2.20, 8df, P = 0.059), carotenoid content (t = -5.68, 8df, P < 0.001) and predawn leaf water potential (t = 4.25, 8df, P = 0.011) when compared to trees sampled on farmland. E. sideroxylon trees sampled close to a farm dam in the West Wits mining district displayed differences in predawn leaf water potential (t = 69.32, 8df, P < 0.001) and carotenoid content (t = -2.13, 8df, P = 0.066) when compared to stressed trees further upslope away from the water source. Multiple linear regressions revealed that the predawn leaf water potential greenness normalised difference vegetation index model, and the predawn leaf water potential water band index model were the “best” surrogate measures of plant water stress when using broad band multispectral satellite and narrow-band hyperspectral satellite data respectively. It was concluded from these investigations that vegetation indices designed to capture changes in plant water content/plant water status and spectral changes in the red edge region of the spectrum, performed well when applied to high spectral resolution remote sensing data. The greenness normalised difference vegetation index was considered to be a fairly robust index, which was highly correlated to chlorophyll fluorescence and predawn leaf water potential. It is recommended that this index has the potential to be used to map spatial patterns of winter-time plant stress for different genera/species and in different geographical locations. Airborne remote sensing surveys were conducted to investigate the application of high spatial resolution remote sensing data to detect plant water stress. Multispectral airborne imagery was acquired by Land Resource International (PTY) Ltd, South Africa. Ground-based measurements of plant water stress were carried out during July and August 2005.Four individual spectral bands and two vegetation spectral reflectance indices, which are sensitive to changes in plant pigment content, were derived from the processed multispectral images viz. red, green, blue and near-infrared spectral bands and the normalised difference vegetation index (NDVI) and greenness normalised difference vegetation index (GNDVI).The results of the multispectral airborne study revealed that carotenoid content together with the green spectral waveband resulted in the “best” surrogate measure of plant water stress when using broad-band multispectral airborne data. Airborne remote sensing surveys were conducted by Bar-Kal Systems Engineering Ltd, Israel, to investigate the application of hyperspectral airborne imagery to detect plant water stress. Six vegetation spectral reflectance indices designed to capture changes in plant pigment and plant water status/content, were derived from the processed hyperspectral images. When using airborne hyperspectral data, predawn leaf water potential with the normalized difference water index was selected as the most appropriate model. It was concluded, upon evaluation of the multiple linear regression models, that the airborne hyperspectral data produced several more regression models with higher adjusted R2 values (Ra2 range 6.2 - 76.2%) when compared to the airborne multispectral data (Ra2 range 6 - 50.1). Exploration of relationships between vegetation indices derived from leaf-level, satellite and airborne spectral reflectance data and ground-based measurements used as “surrogate” measures of plant water stress, revealed that several prominent and recurring spectral reflectance indices could be applied to identify species-specific plant water stress within the Welkom, Vaal River and West Wits mining districts. The models recommended for mapping and detecting spatial patterns of plant water stress when using different sources of remote sensing data are as follows: the chlorophyll b DATT spectral reflectance model when derived from leaf-level spectral reflectance data, can be applied across all three mining districts the predawn leaf water potential GNDVI spectral reflectance model and predawn leaf water potential water band index spectral reflectance model when utilising satellite multispectral and hyperspectral remote sensing data carotenoid content green band spectral reflectance model can be used for airborne multispectral resolution data predawn leaf water potential NDVI spectral reflectance model is best suited for airborne high spatial and hyperspectral resolution data. These results indicate that measurements of predawn leaf water potential and plant pigment content have been identified as key methodologies for ground-truthing of remotely sensed data and can be used as surrogate measures of plant water stress. Some preliminary research was undertaken to evaluate if wood anatomy characteristics could be used as a non-destructive and rapid low-cost survey approach for identifying trees which are experiencing long-term plant stress. Seventy two wood core samples were extracted and analysed. Predawn leaf water potential measurements were used to classify stressed and unstressed trees. Relative differences in radial vessel diameter, vessel frequency and wood density were examined. Comparison of the radial vessel diameter and vessel frequency measurements revealed significant differences in three of the five comparative sampling sites (p <0.05). The results of the density analyses were significantly different for all five comparative sampling sites (p < 0.01). In general, trees experiencing higher plant water stress displayed smaller vessel diameters, compared to less stressed or healthy trees. Sites which were influenced by high levels of contaminated water also displayed smaller vessel diameters, indicating that the uptake of contaminants could affect the wood anatomy of plants. Trees considered to be experiencing higher plant water stress displayed higher vessel frequency. This preliminary study showed that plant stress does influence the wood anatomical characteristics (radial vessel diameter, vessel frequency and wood density) in E. camaldulensis, E. sideroxylon and S. lancea in the three mining districts. Spatial patterns of trees, mapped in the three gold mining districts, Welkom (27º57´S, 26º34´E) in the Free State Province, Vaal River (26º55´S, 26º40´E) located in the North West Province, and West Wits (26º25´S, 27º21´E) located in Gauteng, which were not experiencing winter-time water stress were correlated to site characteristics such as average soil depth, percent clay in the topsoil, groundwater chloride and sulphate concentrations, total dissolved solids, electrical conductivity and groundwater water level. The spectral reflectance model derived between predawn leaf water potential and the green normalised difference vegetation index using broad-band multispectral Proba Chris satellite data was used to map spatial patterns of unstressed trees across the three mining districts. Very high resolution (75 cm) multispectral airborne images acquired by LRI in 2005 were used to demarcate and classify vegetation using the maximum likelihood supervised classification technique. Interpolated surfaces of groundwater chloride and sulphate concentrations, total dissolved solids, electrical conductivity, pH and groundwater table levels were created using the kriging geostatistical interpolation technique for each mining district. Random sample analyses between stressed and unstressed trees were extracted in order to determine whether site characteristics were significantly different (using t-tests). Site characteristic surfaces which were significantly different from stressed areas were spatially linked to trees which were not experiencing winter-time plant water stress for each tree species investigated in each mining district. This spatial correlation was used to make recommendations and prioritise sites for the establishment of future block plantings. Analysis of the site characteristic data and the geophysical surveys undertaken in the three mining districts which provided detailed information on groundwater saturation and an indication of the salinity conditions, confirmed the presence of relatively shallow and saline groundwater sources. This would imply that tree roots could access the relatively shallow groundwater even during the dry winter season and assist in containing contaminated groundwater seeping into surrounding lands. Keywords : airborne imagery, ground-based measurements of plant water stress, hyperspectral, leaf-level spectroscopy, multispectral, satellite imagery, spatial patterns of unstressed trees, spectral reflectance indices

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016.
Gold mining of the Witwatersrand Basin reefs has been responsible for the rise of Johannesburg as an economic centre of South Africa. While mining provided a base for business and infrastructure development for the region, it has also generated social and environmental problems for the country. Tailings storage facilities (TSFs), a common sighting around Johannesburg and across the entire basin, have been built to contain the processed waste following extraction of gold from the pyrite containing quartzite ore. When the fine grained waste is exposed to atmospheric conditions, oxidation of remnant sulphides occurs resulting in acidic, metal rich and sulphate rich plumes that enter the environment through surface and groundwater systems. This thesis sought to better understand the release, transport, dispersal and fate of metals emanating from TSFs and their remnant footprints on the Witwatersrand. These metals included aluminium, copper, chromium, iron, manganese, nickel and uranium and are known to be toxic to humans depending on their concentration and speciation. Traditionally, analytical methods have been employed in studies focussing on the characterisation of some of these processes in the region. While these studies have generally conducted quantitative assessment of the extent of pollution, little comprehensive interrogation and fingerprinting of the processes that are influential in determining the potential risk posed by metals has been done. This has largely been due to the shortcomings of analytical methods to determine these. To this end, this research has employed geochemical modelling to complement the traditional analytical methods. The approach to study the release of metals from TSFs involved assessment of the partitioning of metals within tailings and their potential release using batch and sequential extraction methods. Processes of metal release within the tailings were simulated through geochemical modelling (using the PHREEQC and Geochemist’s Workbench codes). The simulations were based on the percolation of rainwater through these layers and the changes in its chemistry along the path. The potential seepage of this plume along the path was then correlated to observed efflorescent mineral crusts that are temporary sinks for metals and are a common feature in the vicinity of the tailings and water bodies such as ponds and streams. The potential impact of the mineral crusts on the water chemistry of receiving water systems following their dissolution was assessed using forward geochemical modelling. The transport of the metals in groundwater was also studied. This involved simulations of the transition in chemistry of a plume from a TSF along an aquifer of known composition. This was based on a 1-D reactive transport model constructed using information from sequential extraction work on the aquifer rock (to identify the key minerals to consider) and site data (mainly flow rates) from previous studies. The processes occurring in the removal of metals from acid mine drainage (AMD) through a permanent sink in the form of a pump-and-treat plant in the Central Goldfield of the basin were simulated using PHREEQC. The findings from the research showed that two different plumes were produced from an abandoned TSF as a result of rainwater percolation, notably a plume produced from the dissolution of secondary salts formed in the oxidised layer and a sulphuric acid rich plume in the unoxidised layer. These differences were apparent in the geochemical composition of the mineral crusts collected on the walls of tailings dumps and from a pond into which the plumes were draining. On dissolution, mineral crusts were found to produce acidic solutions with crusts containing predominantly Fe producing pH values below 3. The simulated dissolution of various types of mineral crusts gave insight into the impact of minerals present in the smallest amount. This showed that the bulk mineralogy as determined by analytical techniques such as PXRD and remote sensing could not be used with confidence to deduce the impact of the mineral crusts on receiving water bodies. The characteristics of surface plumes released from tailings TSF were compared to other water systems in the area around Soweto, with complementary interpretation conducted using chemometric methods. From principal component analysis (PCA), surface water systems were found to form distinct groups largely influenced by mineral solubility, alkalinity and dissolved oxygen content. The 1-D reactive transport simulations involved acidic, metal and sulphate rich water ingressing the aquifer (below the TSF). Several scenarios were modelled including simulations with different dolomite contents; allowing for surface complexation and the presence of cation exchange surfaces. At a point 500 m from the water ingress in the dolomite rich aquifer, Fe and Mn were largely precipitated out (as confirmed by sequential extraction results on the aquifer rock) while the sulphate concentration was reduced by almost half. On the other hand, Ca concentrations were conservative largely because of continuous dissolution of dolomite and precipitation of gypsum along the flow path. The simulations of the high density sludge treatment plant involved forward modelling of the treatment process with the sludge responsible for the removal of trace metals from the incoming acid mine drainage. The model can be of use for cost and process optimisation at the facility. This research has had notable outputs in the form of publications; models on metal release, transport and attenuation; and models on pump-and-treat processes. These will form an important repository of information and for benchmarking any further studies related to AMD.
MT2016