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*Blend B – Use when water quality treatment (phosphorus, metals) is the priority and more diverse planting options are desired. Consists of 3 parts sand to 2 parts topsoil to 1 part organic material/additives.
*Blend B – Use when water quality treatment (phosphorus, metals) is the priority and more diverse planting options are desired. Consists of 3 parts sand to 2 parts topsoil to 1 part organic material/additives.
See [[Filter media]] for detailed guidance on different blends, required performance criteria, and specifications and laboratory tests for blend components and the filter media itself.
See [[Filter media]] for detailed guidance on different blends, required performance criteria, and specifications and laboratory tests for blend components and the filter media itself.
===Geotextile===
To avoid clogging, the use of geotextile should be avoided exept for a strip over the perforated pipe or on the sides of the bioretention if necessary. For pipes with 360° perforations place a strip of geotextile over the pipe to reduce the migration of fines from overlying media. Geotextile used for weed control (i.e. landscape fabric) in filter bed media or under mulch should be avoided.
Geotextile that is used should have material specifications that conform to Ontario Provincial Standard Specification (OPSS) 1860 for Class II geotextile fabrics. Should be woven monofilament or non-woven needle punched fabrics.
===Choker Layer===
A minimum 100 mm deep layer of clean 5 to 20 mm diameter angular or rounded stone (e.g. High Performance Bedding, HL-6, pea gravel) should be placed on top of the coarser storage reservoir aggregate to prevent downward migration of filter media into the reservoir and pipe. See [[Aggregates]].
===Storage reservoir===
Should be a minimum of 300 mm deep, and filled with granular material of washed 25 or 50 mm diameter crushed angular stone (max. wash loss of 0.5%). Include organic material derived from untreated wood (e.g. chips, mulch or shavings) to enhance nitrogen removal. Also see [[Internal water storage]]. See [[Bioretention: Sizing]] for reservoir sizing guidance, including depth and area of surface ponding and reservoir volume needed to capture and store the design storm.
===Plants===
===Plants===