B-1.1, r. 2 - Construction Code

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8.43. Every excavation in which a tank is installed must have at least one observation well.
The observation well must consist of a perforated pipe at least 150 mm in diameter installed vertically, extending down 900 mm below the bottom of the tank, and be accessible from the ground. The pipe must also be enclosed inside a permeable lining if it is buried in sand.
O.C. 220-2007, s. 1.