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→Backfill Granular and Pipes (JC)
'''Impermeable liner'''<br>
'''Impermeable liner'''<br>
Underdrains are pipes that can be included to collect subsurface water. Their design is determined by the drainage requirements of the feature.
Construction Steps:
*Install the underdrain to grade with a consistent slope of 0.5% to 1.0%
*Connect overflow risers with single-elbowed ‘y’ connections or 45° elbows
*Situate maintenance risers where siltation is expected in drain lines (such as at junctions or where grade and direction changes occur)
*Mark the locations of risers
*Use video inspections to confirm that the interior of the underdrain remains free of debris after construction
Key Inspection Points:
*Size, type, and material of the underdrain conforms to the design specifications
*Underdrain is perforated prior to arrival on-site
*Drain material is resistant to UV radiation and any chemicals in the soil and groundwater
*Clean-outs are positioned correctly and spaced appropriately for the size of the underdrain
*Any manual perforations are approved by the engineer
*Pipe grade matches design specifications
*Tie-in locations to municipal sewers meet City specifications
Mistakes to Avoid:
*Incorrect overflow risers – ensure single-elbowed ‘y’ connections or 45° elbows are used for overflow risers instead of ‘T’ connections
*Incorrect drain size – confirm underdrain has an internal diameter greater than or equal to 200 mm to reduce freezing and allow cleaning and camera inspections
*Potential for clogging – Ensure gravel coverings have not been included with the underdrain
For more information on the design of under-drains, see the page on under-drains.
'''Underdrain'''<br>
'''Underdrain'''<br>
Impermeable liners can be applied when LID features are not intended to infiltrate runoff into the underlying soil. Where building foundations that are adjacent to the LID feature are not waterproofed, liners can be used to protect neighbouring infrastructure.
Construction Steps:
*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
*Place lengths of liner on the bed of the facility as per the manufacturer’s specifications
*Provide 150 mm of overlap between adjacent lengths of liner
*Secure liner in-place and bond together the overlapping portions of liner as specified by the manufacturer
*Where pipes provide drainage from the practice, a flange should be sealed to the pipe and liner.
*Compact sand or apply cushion fabric on top of the liner to protect against punctures
Key Inspection Points:
*Liner is confirmed to match design specifications
*Liner installation conforms to manufacturer’s specifications
*Minimum overlap with
*Need for impermeable liner is confirmed through field verification of setbacks to adjacent infrastructure
*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 contamination
For more information on impermeable liners, see the page on liners.
'''Overflow or Overflow Drain'''<br>
'''Overflow or Overflow Drain'''<br>
'''Monitoring well'''<br>
'''Monitoring well'''<br>