MIGRATION OF LANDFILL LEACHATE INTO A SHALLOW CLAYEY TILL IN SOUTHERN NEW BRUNSWICK - A FIELD AND MODELLING INVESTIGATION

摘要

The Fredericton Region Solid Waste Commission landfill site in southern New Brunswick is located on a Wisconsinan silty clay till deposit having a thickness of at least 10 m. Data from 36 existing wells, together with 9 wells constructed as part of this research, were used to establish hydrogeological conditions at the site. Near the landfilled wastes the most significant hydraulic gradients are vertically downward. To assess the extent of vertical leachate migration, continuous samples of the shallow till were obtained horn beneath the landfilled wastes and at selected locations not affected by landfilling. These samples were subsectioned, and extruded pore waters were analysed for nine leachate species. The field profiles for chloride and dissolved organic carbon were compared with simulated profiles generated using a fractured - porous media transport model. The results from this comparison indicated that the upper 4 m of the till can be adequately represented using an equivalent porous medium approach; this is a result of extensive fracturing of the till. In calibrating a one-dimensional porous media transport model to the observed chloride profile, values for the advective velocity (0.7 m/year) and dispersive parameters for these regionally important till deposits were obtained. Advection and mechanical dispersion are clearly more important than molecular diffusion, and thus for shallow depths the tills cannot be considered as diffusion barriers. The results of the modelling indicate that chloride migrated to a maximum depth of about 6 m during the 6 years since landfilling began. There is currently little information on the deeper (less than or equal to 5 m) tills, and thus it is not known if our findings can be extrapolated to greater depths. [References: 31]