Design and construction of the barrier system for the Halton Landfill

Considerations related to the design of the Halton Landfill as a "hydraulic trap" are summarized together with the research that was conducted to supp ort the design concept. The interrelationship between hydrogeology and the engineered design is examined. Laboratory experiments demonstrated that the re can be diffusion away from a source, even with significant inward veloci ty. Existing theory was found to provide a good prediction of the observed concentration profile in these experiments. It is also shown that a pressur ized air pocket below the clay effectively acts as a zero-flux boundary and hence, with respect to migration of chloride, could be conservatively negl ected in the impact assessment. The results of the impact calculations pred ict only a small increase in chloride concentration in the receptor aquifer while there is negligible predicted impact due to organic contaminants. Th e landfill was designed and constructed with a granular "sub-liner continge ncy layer" (SLCL) beneath the compacted liner. The operation of this layer is discussed. Finally, the construction of the compacted clayey liner with a hydraulic conductivity of 1 10(-8) cm/s is documented.