Changes

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Filter media should be obtained premixed from a vendor and meet all municipal, provincial and federal environmental standards. Topsoil used to produce the mix should be passed through a 5 centimetre (2 inch) screen to remove large rocks, roots and other debris, while retaining soil peds. Samples of the filter media should be dried, ground and tested by a certified soil testing laboratory to ensure they meet the following specifications:

Filter media should be obtained premixed from the vendor and meet all municipal, provincial and federal environmental standards. To minimize transportation-related environmental impacts, filter media should be obtained from local vendors and blended from locally sourced materials.  Topsoil used to produce the mix should be passed through a 5 centimetre (2 inch) screen to remove large rocks, roots and other debris, while retaining soil peds. Samples of the filter media should be dried, ground and tested by a certified soil testing laboratory to ensure they meet the following specifications:

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===Organic component alternatives===

===Organic component alternatives===

Even low-phosphorus composts are known to export phosphorus over many years. The use of compost is not recommended in nutrient-sensitive watersheds where phosphorus pollution is a concern, or an [[Additives| additive]] to enhance nutrient retention of the media should also be included (see below). There are a number of alternative sources of soil organic matter which have undergone field studies which have benefits and potential concerns:

Even low-phosphorus composts are known to export phosphorus over many years. The use of compost is not recommended in nutrient-sensitive watersheds where phosphorus pollution is a concern, or an [[Additives| additive]] to enhance nutrient retention of the media should also be included in the blend, or a layer be included above the stone reservoir, or a reactive media vault be included in the treatment train downstream of the bioretention (see Additive below for available options). There are a number of alternative sources of soil organic matter which have undergone field studies which have benefits and potential concerns:

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!Peat moss

!Peat moss

|Doesn't leach phosphorus||Must be extracted from natural wetlands

|Doesn't leach phosphorus||Must be unsustainably extracted from natural wetlands

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!Shredded paper (e.g., Pittmoss)

!Shredded paper (e.g., Pittmoss)

{{:Additives}}

{{:Additives}}