Modelling of contaminant transport within a marshland environment

Since the early 1980s, leachate originating from the Alice and Fraser Municipal Landfill site, an active landfill site located near Pembroke, Ontario, has been discharged into a natural marshland system located some 300 m down-gradient from the waste disposal site. However, monitoring of the water quality within the marshland indicates that the contaminant level has not yet surpassed the background concentration values downstream from the main impacted area. A mathematical modelling procedure was developed in an attempt to predict the mobility of several contaminant species within the marshland environment. Parameters needed for the predictive model were gathered based on the physical configuration of the landfill and marshland as well as associated laboratory-derived data on the attenuation capacity of the marshland soil matrix. A multidimensional finite-difference model based on the Advection-Dispersion equation was used to predict migration of the contaminants. The model was adapted to the hydrologic characteristics of the marshland, emphasizing groundwater flow, dilution and the adsorption capacity of the organic soil. The surface water flow in the marshland was assumed to be at the marshland surface, i.e. only the groundwater flow in the organic soil layer was considered in this investigation. Modelling results indicate that marshland soil has the capacity to substantially retard the migration of several contaminant species typically found in landfill leachate.