An evaluation of the effectiveness of the bentonite seals in groundwater monitoring wells

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University of New Brunswick


Evaluating the effectiveness of the bentonite seal in groundwater monitoring wells was conducted in two parts. The first determined a minimum seal setting time of 24 hours by conducting shear strength tests on the swollen bentonite material. These tests were accomplished by removing metal bars that were placed in bentonite seals that had various setting times. The average shear strength value of 8.2 kPa from the experimental data is within the published range of 3.38 to 27.30 kPa. The second part involved testing bentonite seals (100 mm dry thickness) with the aid of a simplified and controlled monitoring well installation in the laboratory. An average minimum hydraulic conductivity was calculated to be 0.776 x 10"7 cm/s at 120 hours. Literature suggests that bentonite alone forming a seal should be impermeable (Grim and Guven, 1978). The apparent hydraulic conductivity values obtained in this experiment are thought to be from leakage between the plexiglass cylinder and seal. Further research should be conducted with an apparatus that better approximates field conditions and various seal thicknesses.