The impact of synthetic leachate on the hydraulic conductivity of a smectitic till underlying a landfill near Saskatoon, Saskatchewan

Abstract

The impact of leachate on the hydraulic conductivity, k, of a glacial till used in the contraction of a liner for a landfill near Saskatoon, Saskatchewan, is evaluated. Low-gradient triaxial permeability testing of the water-moulded till over a 7-month period with six pore volumes of test leachate at a hydraulic gradient of approximately 100 gave a hydraulic conductivity of 3.0 × 10−9 cm/s, compared with 6.0 × 10−9 cm/s for the water-permeated sample at the same gradient. The k was also evaluated at gradients of 20 and 50 during water permeation and found to be 8.0 × 10−9 and 6.8 × 10−9 cm/s, respectively. The slight decrease in k with increase in gradient was attributed to a decrease in void ratio, resulting from a net increase in applied effective stress at the outflow end of the specimen. An assessment of the clay mineral composition of the till at the end of permeability testing did not show collapse of the smectite peak. Instead, the leachate appeared to have actually enhanced the smectite peak relative to the illite peak. It was concluded that the leachate did not have any detrimental impact on the till and that the hydraulic conductivity "of the 0.3-m-thick liner underlying the landfill may not be expected to increase as a result of interaction with leachate. Key words: leachate, soil liners, hydraulic conductivity, smectitic till, X-ray diffraction, triaxial permeability testing.