Hydrogeological Considerations for Landscape Reconstruction and Wetland Reclamation in the Sub-humid Climate of Northeastern Alberta, Canada

• Author / Creator

  Twerdy, Pamela

• Oil sands mining companies must reclaim tailings deposits to equivalent land capability in Alberta’s boreal forest. Post-mining landscapes should be reconstructed to promote the development of hydrologic systems that can sustain reclaimed ecosystems in a sub-humid climate, while limiting migration of salts from underlying waste materials. However, landform design requirements that foster the development of appropriate near-surface hydrologic flow systems are poorly understood. Syncrude Canada Ltd. constructed Sandhill Watershed (SHW), a 52 ha coarse-textured upland/lowland complex overlying a deep tailings deposit, to explore the influence of landform characteristics, reclamation cover choices and vegetation densities on reclamation performance.

  This study examines the hydrogeologic characteristics of SHW and explores the resulting groundwater flow system in the years following its construction. Field measurements collected from May to October (2015 to 2017), from 230 shallow piezometers, including groundwater measurements (water level, temperature, and electrical conductivity), water samples and soil saturation maps were used to characterize the hydrogeology. A subset of data, including stable water isotopes and elemental chemistry, were collected during 2017 to resolve the mechanisms leading to observed solute distributions. Field observations were used to calibrate a three-dimensional steady-state numerical groundwater flow model to evaluate present and possible future hydrologic systems.

  A shallow groundwater system dominated by lateral flow developed within SHW. The flow system is strongly influenced by hydraulic conductivity and appears to have negligible inputs from deeper groundwater. Most recharge originates from a laterally extensive upland feature coinciding with the adjacent groundwater divide, beyond the southern extent of the study area. Shallow water tables near, and standing water in, the lowlands are most sensitive to precipitation. Overall, solute concentrations increase with depth in the watershed; however, areas with shallow water tables and shallow slopes are prone to developing elevated solute concentrations following precipitation events. Analyses indicate water table configurations responded dynamically to variable recharge rates associated with the depth to water table, and reclamation prescriptions for soil and vegetation.

  These results indicate fresh shallow groundwater systems can develop for wetland reclamation in post-mining reconstructed landscapes. By appropriately sculpting coarse-textured construction materials during landform design, a freshwater lens developed at the water table beneath hummocks where groundwater is approximately 2 m below ground surface; here, the vertical geochemical gradient transitions from mixed-fresh groundwater to Na+ Cl-/SO4 2- enriched groundwater approximately 1.8 m below water level. Sloped areas with shallower water tables that fluctuate within the rooting zone tend to have elevated solute concentrations near the water table, especially following precipitation influxes, due to lateral groundwater seepage, groundwater ridging and evapoconcentration. These results provide guidance for designing future coarse-textured landforms and developing hydrologic systems for boreal forest reclamation. In particular, designers should reconstruct watersheds that promote groundwater recharge in upland areas by building lower and more laterally expansive hummocks than those in SHW to support water tables approximately 2 m BGS. Furthermore, the interface between the uplands and lowlands should be abrupt, to limit the extent of seepage faces. With these slight landform modifications, recharge and solutes can be better managed to allow the shallow groundwater system to remain fresh, while sustainably sourcing water to down gradient environments.

• Subjects / Keywords

  • Athabasca Oil Sands Region
  • hydrogeology
  • reclamation
  • landscape reconstruction
  • tailings

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-zpg2-6p77

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.