Changes

*Perforated pipes should be continuously perforated, smooth interior HDPE (or equivalent material) with a minimum inside diameter of 100 mm. **Where freezing is a concern, horizontal underdrain pipes should be over-sized to a minimum 200 mm diameter.  

*Perforated pipes should be continuously perforated, smooth interior HDPE (or equivalent material) with a minimum inside diameter of 100 mm.  

**Where freezing is a concern, horizontal underdrain pipes should be over-sized to a minimum 200 mm diameter.  

**Perforations should be 10 mm in diameter and distributed at least every 90 deg around the pipe.

**Perforations should be 10 mm in diameter and distributed at least every 90 deg around the pipe.

*All underdrains should be capped on the upstream end.

*All underdrains should be capped on the upstream end.