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  • Canadian Science Publishing  (6)
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  • 1
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    Overwinter soil nitrogen dynamics in seasonally frozen soils (2000)
    Canadian Science Publishing
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    Publication Date: 2000-11-01
    Description: An overwinter soil-monitoring study was conducted at two sites in southern Ontario. Soluble soil N accumulation at both sites occured in early winter, peaked when soil water was frozen, and then declined during the period that frozen soil water was present. The amount of soluble soil N accumulated was 48 ± 12 kg N ha−1 at one site, and 21 ± 6 kg N ha−1 at the other. In both cases, the overwinter accumulation approximately doubled the amount of soluble N in the soil. Similar trends were observed in both mineral and organic N, with 60 to 74% of the accumulation occurring in the organic form. No clear correlations between soluble nitrogen dynamics and soil extractable organic carbon or soil microbial biomass carbon dynamics were observed. Denitrification apparently occurred in shallow soil during the thaw period at one site. Since soil nitrate levels decreased before significant thawing occurred, leaching was probably not the primary dissipation mechanism. We hypothesize that the soluble N accumulation was due to death and lysis of soil microorganims during freezing and thawing. The presence of soil ice apparently decreased the lethality of the soil enviroment, allowing N dissipation to occur. Soil N dissipation could be due to gaseous losses, and is likely related to significant N2O fluxes commonly observed during spring thaw. Key words: Nitrogen, overwinter, soil ice
    Print ISSN: 0008-4271
    Electronic ISSN: 1918-1841
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 2
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    Diffusion of nonreactive and reactive solutes through fine-grained barrier materials (1984)
    Canadian Science Publishing
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    Publication Date: 1984-08-01
    Description: In many cases where fine-grained geologic materials are used as barriers to the migration of contaminated fluids, the principal mechanism of contaminant transport is molecular diffusion. Thus the effective molecular diffusion coefficient is the parameter of greatest importance when predicting migration rates and contaminant fluxes. Diffusion coefficients were measured for two non-reactive solutes (36Cl and 3H) and one reactive solute (85Sr) in seven mixtures of bentonite and silica sand ranging from 0 to 100% bentonite by weight. Tortuosity factors were calculated from the results of the nonreactive diffusion experiments, and retardation factors for the reactive solute from measured distribution coefficient (Kd), bulk density, and porosity values. The results showed the diffusive transport of both the reactive and nonreactive solutes to be consistent with a Fickian diffusion equation. For practical purposes, and at the low values of bulk density used in the experiments, the effective diffusion coefficient of the reactive solute could be calculated with a reasonable degree of certainty from the measured retardation factor and an estimated value of tortuosity. The results showed that because of the interaction between the distribution coefficient, bulk density, and porosity, an increase in clay content beyond about 5–10% did not result in a further reduction of the diffusion coefficient of the reactive solute. Key words: diffusion, adsorption, retardation, tortuosity, clay liners.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 3
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    Numerical simulations to investigate moisture-retention characteristics in the design of oxygen-limiting covers for reactive mine tailings (1991)
    Canadian Science Publishing
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    Publication Date: 1991-06-01
    Description: Acid generation in reactive mine tailings is an oxidation process that is dependent on availability of molecular oxygen. As a consequence of the diffusion coefficient of oxygen being several orders of magnitude higher in air than in water, influx of atmospheric oxygen into a material at depth can theoretically be minimized by maintaining a protective cover layer at high moisture content. Such oxygen-limiting covers are generally of finer texture than the material being protected. A numerical model was used to investigate the importance of moisture-retention characteristics in the transient drainage of such two-layer systems. The results show that the effectiveness of a material as a moisture-retaining cover is dependent on the magnitude of its air-entry value. The thickness of the cover maintained at full saturation after prolonged drainage also depends on the pressure head at which the underlying material approaches residual saturation. Key words: geologic covers, tailings, numerical simulations, air-entry value, residual saturation, textural layering.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 4
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    Fracture effects in the shallow groundwater zone in weathered Sarnia-area clay (1989)
    Canadian Science Publishing
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    Publication Date: 1989-02-01
    Description: The Sarnia area of southwestern Ontario is underlain by thick deposits of clay-rich glacial till. From ground surface to between 4 and 6 m depth the clay till is fractured, oxidized, and penetrated by root holes. The water table fluctuates seasonally between the ground surface and the bottom of the weathered zone. Water-level response tests in conventional piezometers installed in augered holes in the weathered zone typically provide very low values of hydraulic conductivity (10−7–10−9 cm/s), which are similar to values obtained from the deeper unweathered and unfractured till. The augering process creates a smeared clay zone along the borehole walls that significantly reduces measured hydraulic conductivity values. In this study, the weathered-zone hydraulic conductivity was measured using unconventional piezometers, a large-diameter well, and a tracer experiment between two test pits. The smeared zone was removed or reduced around these installations, and the measured weathered-zone hydraulic conductivity was 10−5–10−7 cm/s, much higher than in the deep unweathered clay. These results, together with depth profiles of groundwater tritium and monitored water-level fluctuations, indicate that the weathered zone has hydraulic conductivity governed by fractures and has significant hydrologic activity in the fractures. Key words: clay, fractures, hydraulic conductivity, permeability, piezometer, tritium, tracer experiment, weathered zone.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 5
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    Distribution coefficients for strontium and cesium in overburden at a storage area for low-level radioactive waste (1985)
    Canadian Science Publishing
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    Publication Date: 1985-02-01
    Description: Distribution coefficients for strontium and cesium, as one component of a hydrogeological site investigation, were determined by the batch method on 12 samples of glacial till and 7 samples of sand from the radioactive waste operations site 2 of the Bruce Nuclear Power Development. The tests were performed using two types of equilibrating solutions traced with radioisotopes; one was a solution with cation concentrations equal to the concentrations obtained in 1:1 solid–solution extracts and the other was natural groundwater obtained from piezometers at or near the depths from which the soil samples were obtained. The measured Kd values were relatively uniform within an individual hydrogeological unit, and differences between units were related to the chemical properties of both the solid and solution phases. The Kd values for both Sr and Cs obtained in the tests performed using the synthetic solutions differed from those obtained in tests using natural groundwater. The differences appeared to be related to the major chemistry of the test solutions and indicated that, to obtain Kd values that were most representative of the in situ conditions, natural groundwater should be used in the batch procedure.The measured Kd values, when used in the linear retardation equation, indicated that in the till materials, 90Sr would migrate at a rate no greater than 0.2 cm∙year−1 and 137Cs would migrate at a rate no greater than 0.001 cm∙year−1. Based on the relatively high Kd value for Cs in the sand (300 mL∙g−1), 137Cs migration through the sand unit would be of little environmental concern. On the other hand, the relatively low Kd for Sr (2 mL∙g−1) indicates that attention should be paid to the pathway role of the sand layer in any assessment of the isolation capability of the site.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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  • 6
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    Evaluation of distribution coefficients for the prediction of strontium and cesium migration in a uniform sand (1982)
    Canadian Science Publishing
    Details
    Publication Date: 1982-02-01
    Description: The validity of using a distribution coefficient (Kd) in the mathematical prediction of strontium and cesium transport through uniform saturated sand was investigated by comparing measured breakthrough curves with curves of simulations using the advection-dispersion and the advection equations. Values for Kd were determined by batch equilibration tests and, indirectly, by fitting the mathematical model to breakthrough data from column experiments. Although the advection-dispersion equation accurately represented the breakthrough curves for two nonreactive solutes (chloride and tritium), neither it nor the advection equation provided close representations of the strontium and cesium curves. The simulated breakthrough curves for strontium and cesium were nearly symmetrical, whereas the data curves were very asymmetrical, with long tails. Column experiments with different pore-water velocities indicated that the shape of the normalized breakthrough curves was not sensitive to velocity. This suggests that the asymmetry of the measured curves was the result of nonlinear partitioning of the cations between the solid and liquid phases, rather than nonequilibrium effects. The results indicate that the distribution coefficient, when used in advection-dispersion models for prediction of the migration of strontium and cesium in field situations, can result in significant error.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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