148-Groundwater Contamination Modelling Underneath Regina Landfill.

Abstract

A three-dimensional finite difference regional groundwater model for the aquifers underlying the Regina area is developed. The conceptual model consists of four hydrogeological layers. Specifying zones of constant properties defined aquifer heterogeneities. The initial groundwater flow model conditions were based on hydraulic heads during the period 1977-1987. The model was calibrated by transient calibration for the period of 1987-1999 and generally produced water levels in the continuously monitored wells. Calibration of the transient flow model using trial and error resulted in 10 hydraulic conductivity zones. Contaminant transport studies from the landfill entailed construction of a local model for the areas surrounding the landfill. The Modflow output was used along with MT3D for contaminant transport studies for contaminants starting from the landfill to the sand zone of the Condie aquifer and the transport of contaminants from the PCC sewage reservoir through the gravel core of the condie moraine. The modeling study was initiated with the migration and transport of chloride representing advective dispersive transport of contaminants without any added reactive effects. Pertinent data and transport modeling reveal that the impact from the landfill towards chloride contamination of the aquifer is in the form of a series of intermittent slugs originating from discrete points in the landfill. The slugs will cease to form once the landfill has been fully covered. Bulk of the chloride from the east of the landfill has been seen to be moving through the continuous gravel core existent through the central part of the Condie moraine. The impact has been seen to have reduced in the past decade with reduced concentration values recorded in monitoring wells reaching the gravel core of the condie moraine as the source have stopped their practice of disposing their sewage into the clay aquitard. Flow and transport parameters are arrived at by a separate sensitivity analysis of the model results with respect to chloride concentrations recorded in monitoring wells showing the impact of the landfill for the period 1990-2000 rather than using plume configurations as there aren't enough monitoring wells in the landfill to reveal an exact shape. The effect is not modeled as there is no identifiable source upstream of the landfill other than the PCC.