HYDRAULIC CONDUCTIVITY AND DIFFUSION MONITORING OF THE KEELE VALLEY LANDFILL LINER, MAPLE, ONTARIO

The 99-ha Keele Valley Landfill is located in a former sand and gravel pit at Maple, Ontario. The base and sides of the pit are lined with a minimum of 1.2 m of excavated clayey silt till recompacted to achieve a design hydraulic conductivity of 1 x 10(-8) cm/s or less. Extensive construction controls and monitoring programs have been implemented t o determine the hydraulic conductivity and advective performance of th e liner. A total of 267 postcompaction laboratory hydraulic conductivi ty (k) tests indicated that the first two stages of the liner had a ge ometric mean k of 7.7 x 10(-9) cm/s. Calculations of in situ hydraulic conductivity based on lysimeter effluent collection rates show decrea ses in k to field values close to the laboratory values. In situ elect rical conductivity sensors and lysimeter effluent chemistry measuremen ts have monitored the advance of leachate-derived chemicals into the l iner. Concurrent field verification by liner exhumation and chemical a nalysis has confirmed the importance of diffusion as the dominant migr ation mechanism through this low-k liner. Similar concentration trends for major ions have been observed in the field lysimeter effluents, e ffluents from laboratory liner-leachate compatibility tests, and pore water extracted from core samples of sections of exhumed liner exposed to leachate. The multicomponent field and laboratory testing and moni toring programs have shown good cross-agreement, and the actual perfor mance of the liner has been close to preconstruction predictions.