*Where freezing is a concern, horizontal underdrain pipes should be over-sized to a minimum 200 mm diameter.
*Where freezing is a concern, horizontal underdrain pipes should be over-sized to a minimum 200 mm diameter.
*Perforations should be made on all sides of the pipe and provide a ≥ 1 m<sup>2</sup> of open area per linear meter of pipe.
*Perforations should be made on all sides of the pipe and provide a ≥ 1 m<sup>2</sup> of open area per linear meter of pipe.
**A perforated pipe with many rectangular slots has better drainage characteristics than a pipe with similar open area provided by fewer circular holes <ref>Hazenberg, G., and U. S. Panu (1991), Theoretical analysis of flow rate into perforated drain tubes, Water Resour. Res., 27(7), 1411–1418, doi:10.1029/91WR00779.</ref>.
*Non-perforated pipes should be used for conveyance to and away from the facility, including overflow.
*Non-perforated pipes should be used for conveyance to and away from the facility, including overflow.
*a perforated pipe with many rectangular slots has better drainage characteristics than a pipe with similar open area provided by fewer circular holes <ref>Hazenberg, G., and U. S. Panu (1991), Theoretical analysis of flow rate into perforated drain tubes, Water Resour. Res., 27(7), 1411–1418, doi:10.1029/91WR00779.</ref>.