An evaluation of the effectiveness of the bentonite seals in groundwater monitoring wells
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Date
1995
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Publisher
University of New Brunswick
Abstract
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.