23. The base of the lower composite liner of an engineered landfill with a double liner system installed as provided in section 22 must be situated above the groundwater level. The lowering of the groundwater level by pumping, drainage or otherwise is permitted only on land where the unconsolidated deposits form a natural homogenous layer with a constant hydraulic conductivity of 5 x 10-5 cm/s or less through a minimum thickness of 3 m, the hydraulic conductivity to be established in situ.
Where the unconsolidated deposits meeting the requirements of the first paragraph are at a greater depth, the disposal areas must also have an impermeable sideslope liner system that complies with the requirements of the first paragraph of section 21; excavation in those disposal areas must not compromise compliance with the requirements of the first paragraph as regards the unconsolidated deposits.