Typically 100-150mm deep or as specified in the engineering design. A clean well graded sand material containing less than 2% fines. The transition layer is used to avoid the migration of the filter media into the drainage layer. HiQuality Group transition Layer sand meets the FAWB bridging criteria. D15 (transition layer) = 5 x d85 (filter media) when used with our Bio Plus or Engineered Filtration Media.
Transition Sand in Bio-retention systems
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