From LID SWM Planning and Design Guide
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An impermeable liner is incorporated into non-infiltrating practices such as stormwater planters, and may be applied in permeable pavements installations where separation from the native soils and groundwater is required.

  • Waterproof containment can be created using concrete or a plastic membrane/liner (HDPE or EPDM are common materials).
    • When the membrane is being used directly in the ground, punctures from stones can be prevented by compacting a layer sand (30 - 50 mm) over the soil prior to installing the membrane.
    • Alternatively, a manufactured cushion fabric (geotextile) can be employed for this purpose.
    • The top surface of the membrane must also be protected from stone and gravel being used for inside the BMP. Again, sand or a cushion fabric may be used.
  • When a pipe is used to provide drainage from the practice to an outlet structure or storm sewer, a 'pipe boot' or flange should be sealed to both the pipe and the liner to prevent leaks.