Slide 34 of 52
Notes:
Additional design considerations for the filter medium and bed construction are provided in this slide.
Designers specifying a grass cover crop for sand or organic filter beds should choose an appropriate species which will develop a root system which does not inhibit infiltration. To help ensure that the filter bed will resist clogging on the pocket sand filter, a pea gravel �window� is recommended to cover approximately 10% of the sand bed surface area.
To help extend the design life of the sand filter bed for the underground sand filter a wide mesh geotextile screen should be placed on the surface of the filter bed to trap the large quantities of trash, litter and organic detritus associated with highly urban areas. During maintenance operations the screen is rolled up, removed and cleaned, and reinstalled.
The main collector pipe for underdrain systems should be constructed at a minimum slope of 0.5%. Observation and clean-out pipes must be provided for all underdrain piping.
