Pore water collected from piezometers installed in a thick clay‐rich till were used to compare and evaluate four techniques for obtaining δD and δ18O values in these media. The techniques included mechanical squeezing, centrifugation, azeotropic distillation, and a direct soil‐water equilibration technique. Direct CO2‐core equilibration yielded sufficiently accurate and reproducible δ18O results of pore water in clay‐rich tills. In addition, this method eliminated the need for labor‐intensive complete extraction of water from the geologic media. Mechanical squeezing and centrifugation produced results similar to direct equilibration. However, both of these methods exhibited a greater degree of variability and were laborious and more time consuming. Small differences in δ18O values between piezometer water and equilibrated, squeezed, and centhfuged samples suggested that each method collected different fractions of the clay‐water reservoir. Although these subtle differences were not conclusive, they did suggest the presence of weakly bound water and highlighted the difference between these three techniques for determining the stable isotopic composition of pore water in clay‐rich aquitards. Azeotropic distillation produced a high level of discrepancy in δD andδ18O results compared to the other methods. Incomplete extraction was considered the most probable cause of this error. The results of this study suggested that direct equilibration is the best method for determining detailed δD and δ18O values of pore water in clay‐rich aquitards.

The successful performance of reclamation soil covers over saline‐sodic overburden associated with oil sands mining in northern Alberta, Canada, depends on the dynamics of water and salt migration within these covers. Subsurface flow exerts a significant control on the distribution of soil moisture and salts within reclaimed landscapes. A conceptual model for fracture‐dominated lateral subsurface flow and transport in a sloping clay‐rich reclamation soil cover over saline‐sodic shale overburden was developed based on an interpretation of field observations. This model was then verified through the use of numerical simulations. The conceptual model assumes that lateral subsurface flow is dominated by a preferential flow system and that chemical equilibration between fresh snowmelt water stored in the macropores and higher concentration pore water stored in the soil matrix is nearly instantaneous. Numerical modeling of subsurface flow indicated that the discharge rate and cumulative volume are controlled by the bulk saturated hydraulic conductivity and drainable fracture porosity, respectively. A drainable fracture porosity ranging from 3 to 4% yielded a simulated cumulative discharge similar to measured values. A pseudo‐equivalent porous medium transport model was used to simulate the Na+ concentration of collected subsurface flow with time. General agreement between measured and simulated values demonstrates that discharge concentrations increase as the depth of perched water diminishes with time and water drains through macropores associated with a matrix of higher solute concentrations lower in the cover profile.

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