Evaluation of Contaminant Containment at Regina Landfill

Abstract

Landfill and waste containment facilities are routinely constructed on natural or engineered low permeability barriers placed above or within the vadose zone to prevent contaminant migration into the groundwater system. Numerical estimates of design lives for assessment of barrier system performance are generally acceptable under numerous landfill regulations. Predictive models work under the general assumption that constructed systems will retain their structural integrity over the design life of the landfill and act as leak proof systems. Contrary to the above assumption, barrier performance, whether natural or engineered, at countless landfills and waste disposal sites across North America suggests that these liners tend to act as leak-resistant, and not leak-proof, systems. Across Canada, the designs of these barrier systems at various landfill sites are typically governed by prescriptive engineering design standards as opposed to performance or risk-based standards set by the regulatory agency having jurisdiction over the landfill.

This study investigates the contaminant containment potential of a composite landfill liner system in conjunction with the naturally occurring glacioacustrine clay barrier at the Regina landfill expansion site. Transit time was calculated for the different landfill design types as prescribed under the Saskatchewan Environment Code (SEC) and compared to simulations using two commercially-available, one-dimensional modeling software packages. VZCOMML© a one-dimensional, steady-state, equilibrium partitioning vadose zone model that uses a multi-layered soil column was used to simulate advective flows; and CHEMFLUX, a one-dimensional model to simulate diffusion.

The results suggest that inherent low permeability property of the native barrier underlying the landfill is adequate to prevent potential contamination of groundwater over the “contaminating life span” (Rowe, 2005) of the landfill expansion area. However, the natural barrier has finite hydraulic conductivity and ultimately, over long periods of time, breakthrough will occur due to diffusion. The literature review and modeling investigation indicate that more attention should be directed towards active contaminant removal, treatment, and disposal as opposed to pure contaminant containment at landfill sites over their design life. There seems to be overemphasis on dry tomb designs focused on contaminant containment, liner effectiveness, and review of hydrogeological aspects as key landfill performance indicators. With current trends in innovation and evolution in landfill technologies, landfills should be viewed as solid waste processing facilities and not waste burial sites. This study hypothesises that a systems approach to design and performance evaluation centered on total lifetime contaminant mass management would be more ideal for the Regina Landfill site.