Bioretention: Filter media

Biomedia should be obtained premixed from a vendor and meet all municipal, provincial and federal environmental standards. Mixing of sand, topsoil and compost should be done in a manner that preserves topsoil peds. The mixture should be free of stones, stumps, roots, or other debris larger than 50 mm diameter. Samples of the filter media should be dried, ground and tested to ensure they meet the following specifications:

The following mix utilizes peat moss instead of compost.

• Fine Aggregate Concrete Sand (ASTM C33) (86%)
• Peat moss (12%)
• Imbrium Sorptive®MEDIA (2%)

substituting peat moss for compost, since peat moss has lower phosphorus content than compost and does not leach phosphorus; and including Sorptive®MEDIA to sorb phosphorus and minimize phosphorus in effluent

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

Decayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.