Impermeable liners: Installation

Impermeable liners can be applied when LID features are not intended to infiltrate runoff into the underlying soil. They protect building foundations or other subsurface infrastructure. They also prevent infiltration through contaminated soils. Where building foundations next to the LID feature are not waterproofed, liners can be used to protect adjacent infrastructure.

Construction Steps:

1. Compact 30 – 50 mm of sand over the soil onto which the membrane will be installed to protect against punctures. Alternatively, a geotextile can be used in the place of sand.
2. Place lengths of liner on the bed of the facility as per the manufacturer’s specifications.
3. Provide 150 mm of overlap between adjacent lengths of liner.
4. Secure liner in-place and bond together the overlapping portions of liner as specified by the manufacturer.
5. Seal a flange to the pipe and liner when pipes provide drainage from the practice.
6. Compact sand or apply cushion fabric on top of the liner to protect against punctures.

Key Inspection Points:

• Liner matches design specifications.
• Liner installation procedures conform to manufacturer’s specifications.
• Minimum overlap between lengths of liner is achieved.
• Need for protection of building footprints and adjacent infrastructure confirmed through field verification of setbacks.
• Sand and/or geotextile are applied on both sides of the liner to protect against punctures.
• Lengths of liner are bonded together to ensure protection against groundwater penetration and contamination.

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  An impermeable liner was placed along one side of the LID facility to prevent infiltrated water from contacting the nearby watermain in the road right-of-way, which runs parallel to the feature. (Photo Source: CVC, 2020)

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  Impermeable Bentofix® liner being rolled out in LID practice area. (Photo Source: CVC, 2012)

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

Filter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

Credit Valley Conservation