Permeability protocol for the compacted clay liner at Metropolitan Toronto's Keele Valley Landfill

Abstract

The Provisional Certificate of Approval to construct a sanitary landfill for municipal waste in an old gravel pit in the Oak Ridges Moraine north of Toronto, Ontario, required that a 1.2 m thick compacted clay liner with a permeability of less than 10−8 cm/s should be placed beneath any refuse. Preliminary testing indicated that the native tills from the immediate vicinity were marginally capable of providing such a liner, as long as they were carefully selected and compacted at moisture contents just above optimum values. However, it was clear that the variability of material and (or) testing was such that some liner samples could have permeabilities greater than 10−8 cm/s. Additionally, there was concern that the sampling and testing procedures could affect the results. This paper details the trials which were carried out at the beginning of construction to establish acceptable sampling and testing techniques.These were finally determined to consist of carefully obtained Shelby tube samples, the permeability of which was tested at representative pressures in triaxial cells. The paper then presents the statistical analyses which were used to verify that the overall permeability of the liner is less than 10−8 cm/s. It also outlines other testing and instrumentation which has been undertaken to verify the liner permeability and integrity. It is concluded that, to date, the permeability testing and protocol are suitable control procedures to verify compliance with the condition of the Provisional Certificate of Approval that a liner permeability of 10−8 cm/s be achieved. Key words: clay liner, permeability, protocol, quality control, sanitary landfill, sampling, statistical analysis, testing.