The Deilmann Tailings Management Facility (DTMF) at Key Lake in northern Saskatchewan, Canada, is an active deposition site for uranium tailings and it has been in operation since 1996. In terms of geochemical stability of the tailings, a ferrihydrite secondary phase is utilized for the sequestration of contaminants, such as As, Ni, Mo, and Se, under alkaline and highly oxic conditions. Arsenic is highly abundant in the DTMF tailings and the principal environmental concern is the possibility for leaching of ferrihydrite-attached As into the surrounding environment. Microorganisms can proliferate in a broad range of habitats and their activities are key factors in determining fate and transport of contaminants in various environments. This thesis attempts to obtain insights into the biogeochemical processes that may occur during the early phase of the DTMF’s history that could potentially become significant over extended periods of time that run from 100’s to 1000’s of years. Hence, a primary focus was to characterize microbial diversity and extrapolate their potential functional roles as well as their potential to chemically alter the Eh and ferrihydrite, which are the primary controlling conditions within the DTMF tailings and in the mineral secondary phase, respectively. To achieve these goals, two molecular techniques (clone library construction and Ion Torrent sequencing), a range of conventional culture-based techniques, metabolic assays addressing metabolic transformation and resistance to metals/metalloids, microscopic technique (Confocal Laser Scanning Microscope), spectroscopic analyses (Scanning Transmission X-ray Microscope) and bench-scale microcosm assays were carried out. Culture-dependent and -independent methods revealed that the most prevalent microbial groups in the water column, tailings mass and at the tailings-water interface affiliated into phyla (e.g., Proteobacteria, Actinobacteria, Firmicutes and Bacteriodetes) that have previously been detected at uranium-, heavy metal- and complex hydrocarbon-contaminated sites. Phylotypes closely related to well-characterized sulfate-, thiosulfate- and iron-reducing bacteria (e.g., Desulfosporosinus, Dethiobacter, Geoalkalibacter, Ralstonia, Georgfuchsia) were also detected at low frequency, with the exception of the tailings-water interface where sequences closely related to Desulfosporosinus were abundant. The readily culturable heterotrophs (e.g., Pseudomonas, Arthrobacter, Massilia, Hydrogenophaga, Polaromonas, Bacillus) retrieved from the tailings exhibited reducing/oxidizing capabilities as well as high tolerance to metal/metalloids. Bench scale microcosm assays showed that heterotrophs native to the DTMF site could not only reduce ferrihydrite but could also create highly reducing (< -300 mV) conditions within the tailings amenable to strict anaerobic bacteria such as Desulfosporosinus. STXM image analyses confirmed the presence of reduced iron in close proximity to bacterial cells in biofilm grown in situ and in microcosm tailings, strongly suggesting that ferrihydrite served as electron acceptor during microbial processes. Reduced iron detected in situ also indicated that microscale iron reduction could occur even though macroscale DTMF chemistry remained oxidizing. Overall, the nature of microbial community present in the DMTF system strongly indicated that complex hydrocarbons (e.g., kerosene) discharged into the tailings during processing could potentially support microbial processes that involve Fe and S cycling and that this process could become significant over extended period of times, contributing to arsenic escape into the environment.

The following is a thesis presented on the history, subsurface characterization and settlement analysis of the Conquista Tailings Impoundment located in Karnes City, TX. This research draws information from readily available sources at TCEQ in Austin, Texas. Documents included in this report date back to the mid-1980s and can be as recent as 2011. This thesis will focus on the eastern section of the Conquista Tailings Impoundment and will primarily observe and predict the settlement experienced in this portion of the site. The site has been analyzed using one-dimensional consolidation analysis, based on three (3) loading factors, and has been modeled using finite element analysis aided by the software PLAXIS. The research has justified the magnitude of settlement that has occurred in the area of concern and has provided just reasoning for the events. Further investigations into the subsurface conditions in the eastern portion of the Conquista Tailings Impoundment will be needed to confirm and refine the analysis presented. / text

Philosophiae Doctor - PhD / In Africa as well as in the world, South Africa plays an important role in the mining industry which dates back almost 120 years. Mining activities in South Africa mainly take place in Gauteng Province. Every year millions of tons of rocks are taken from underground, milled and processed to extract gold. Uranium is one of the minerals which is mined as a by-product of gold. The uranium bearing tailings are then placed on large dumps which are usually one or more kilometres in diameter in the environment. There are approximately 250 gold mine tailings dumps covering a total area of about 7000 ha. These gold mine tailings dumps contain considerable amounts of radium (226Ra) and have therefore been identified as large sources of radon (222Rn). Radon release from these tailings dumps pose health concerns for the surrounding communities. This study reports on the 222Rn soil-gas concentrations and exhalations measurements which were conducted at a non-operational mine dump (Kloof) which belongs to Carletonville Gold Field, Witwatersrand, South Africa. Radon soil-gas concentrations were measured using a continuous radon monitor (the Durridge RAD7). The radon soil gas concentration levels were measured at depths starting from 30 cm below ground/air interface up to 110 cm at intervals of 20 cm. These radon soil-gas measurements were performed at five different spots on the mine dump. The concentrations recorded ranged from to kBq.m-3. Furthermore, thirty four soil samples were taken from these spots for laboratory-based measurement. The soil samples were collected in the depth range 0-30 cm and measured using the low-background Hyper Pure Germanium (HPGe) -ray detector available at the Environmental Radioactivity Laboratory (ERL), iThemba LABS, Western Cape Province. The weighted average activity concentrations in the soils samples were Bq.kg-1, Bq.kg-1 and Bq.kg-1 for 238U, 40K and 232Th, respectively. 1 26 23 472 7 308 5 2551 18 The activity concentration of 40K and the decay series of 238U and 232Th for the top 30 cm of the accessible parts of the mine dump were measured using the MEDUSA (Multi-Element Detector for Underwater Sediment Activity) -ray detection system which was mounted on the front of a 44 vehicle, 0.6 m off the ground. The spectra acquired by the MEDUSA system were analysed and the activity concentrations were extracted using the Full Spectrum Analysis approach. The average activity concentrations obtained were 25975 Bq.kg-1 for 40K, 30940 Bq.kg-1 for 238U series and 185Bq.kg-1 for 232Th series for 2002 survey while 26075 Bq.kg-1 for 40K, 31040 Bq.kg-1 for 238U series and 20 5 Bq.kg-1 for 232Th series were recorded for 2010 survey. Moreover, a novel technique by means of the MEDUSA -ray detection system was utilised to map radon exhalation from the Kloof mine dump. In this technique the 214Bi concentration in the top 30 cm of the dump, which is used as a proxy for the 238U or 226Ra concentration, is measured even though there is not secular equilibrium between the radium and bismuth because radon has escaped. The actual activity concentrations of 40K and 226Ra are obtained from soil samples which were collected, sealed and measured in the laboratory settings after attaining secular equilibrium since radon gas does not escape. By comparing the ratios of the activity concentrations of the 214Bi obtained in the field using the MEDUSA -ray detector system to the activity concentrations of the 214Bi obtained in the laboratory using the HPGe -ray detector system yields a reasonable radon exhalation for a particular location in the mine dump. In this case it is assumed that the 40K and 232Th series activity concentrations are not or hardly affected by radon exhalation. By applying this new technique an average normalised radon flux of 0.120.02 and 0.120.02 Bq.m-2.s-1 were obtained for 2002 and 2010 surveys, respectively. The electrets and the IAEA standard formula were also utilised to calculated radon fluxes yielding 0.060.02 and 0.120.02 Bq.m-2.s-1 respectively.