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The Geochemical Evolution of Oil Sands Tailings Pond Seepage, Resulting from Diffusive Ingress Through Underlying Glacial Till Sediments

  • Author / Creator
    Holden, Alexander A
  • Oil sands tailings are comprised of sands, silts, clays, and process-affected water (OSPW). The latter includes high concentrations of dissolved ions, as well as organic contaminants, making the water toxic to aquatic organisms. In Northern Alberta, tailings ponds are being constructed on glacial till, overlying sand channel aquifers, establishing a potential hydraulic connection between the pond and downstream water systems. However, to date, no targeted attempts have been made to characterize the biogeochemical evolution and end products as tailings pond OSPW infiltrates into glacial till prior to reaching these aquifers, thus overlooking a key component of the contaminant transport pathway. Addressing this knowledge gap is a critical step towards protecting aquatic resources. Cation exchange capacity, exchangeable cation, batch sorption and radial diffusion cell experiments and supporting geochemical simulations were conducted: a) to assess the potential for release (or attenuation) of trace elements and major ions from glacial tills when exposed to OSPW; and b) to identify the principal geochemical processes involved in controlling pore water and sediment chemistry. The experiments revealed that sediment-bound cations available for exchange, consisted of Ca>Mg>K>NH4>Na; while the mean cation exchange capacity in the till (Methylene Blue method) was 4.7±2.7meq 100g-1. Results further indicate that the ingress and interaction of OSPW with the glacial till sediment-pore water system will result in: the mitigation of incoming sodium by ion exchange with sediment-bound calcium and magnesium, followed by limited precipitation of calcium and magnesium carbonates; sulfate reduction and subsequent sulfide precipitation; and biodegradation of organic carbon. High concentrations of OSPW chloride (~375mg L-1) are expected to persist. Ion exchange, oxidation-reduction, and mineral phase reactions including reductive dissolution of metal oxyhydroxides influenced trace metal mobility, which is similar to previous observations within sandy aquifer settings. Furthermore, though several trace elements showed the potential for release, large-scale mobilization is not supported. Understanding the environmental impact of tailings seepage is of great importance in managing water resources in Alberta. The present research offers a scientific basis to guide future remediation and reclamation strategies, seepage management schemes, and development of compliance legislation, and is therefore anticipated to have industry-wide benefit.

  • Subjects / Keywords
  • Graduation date
    2012-11
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/R3M13X
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
    English
  • Institution
    University of Alberta
  • Degree level
    Doctoral
  • Department
    • Department of Civil and Environmental Engineering
  • Specialization
    • Geoenvironmental Engineering
  • Supervisor / co-supervisor and their department(s)
    • Ulrich, Ania (Civil and Environmental Engineering)
  • Examining committee members and their departments
    • Mayer, K. Ulrich (Earth, Ocean and Atmospheric Sciences)
    • Siddique, Tariq (Renewable Resources)
    • Wilson, G. Ward (Civil and Environmental Engineering)
    • Weisener, Chris (Earth and Environmental Sciences)
    • Chalaturnyk, Rick (Civil and Environmental Engineering)