BMPs for stormwater infiltration

Best Management Practices that infiltrate stormwater runoff into underlying soil include, but are not limited, to

• infiltration basins,
• infiltration trenches,
• underground infiltration,
• bioinfiltration,
• permeable pavements, and
• tree trenches and tree boxes.

These are discussed briefly below.

Infiltration basin

Photo of an infiltration basin. Source: Clark County, Washington, with permission.

Applications		Treatment capabilities3, 4, 5
Residential	yes	TSS	High6
Commercial	Yes	TN	Medium/high
Unltra-urban	Limited1	TP	Medium/high
Industrial	Yes2	Chloride	Low
Highway/road	Limited	Metals	High
Recreational	Yes	Oils and grease	High
		Pathogens	High
1 Due to a size restriction; 2 Unless the infiltration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. Infiltration BMPs are PROHIBITED in these areas; 3Underground infiltration systems will have different pollutant removal capabilities than what is provided in this table. These systems may have a wider application range, however, there is concern that they do not provide adequate treatment of the pollutants; 4 This is only for the portion of flow that enters the infiltration basin; by-passed runoff does not receive treatment; 5 Low = < 30%; Medium = 30-65%; High = 65 -100%); 6 Assumes adequate pre-treatment

An infiltration basin is a natural or constructed impoundment that captures, temporarily stores, and infiltrates a design volume of water. For more information, see the following pages in this Manual.

• Overview for Infiltration basin
• Design criteria for Infiltration basin
• Construction specifications for Infiltration basin
• Operation and maintenance of Infiltration basin
• Cost-benefit considerations for Infiltration basin
• Calculating credits for infiltration basin
• External resources for Infiltration basin
• References for Infiltration basin
• Requirements, recommendations and information for using infiltration basin/underground infiltration BMPs in the MIDS calculator

Infiltration trench

Photo of a Infiltration trench in Lino Lakes

Applications		Treatment capabilities3, 4
Residential	yes	TSS	High5
Commercial	Yes	TN	Medium/high
Unltra-urban	Limited1	TP	Medium/high
Industrial	Yes2	Chloride	Low
Highway/road	Yes	Metals	High
Recreational	Yes	Oils and grease	High
		Pathogens	High
1 Due to a size restriction; 2 Unless the infiltration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. Infiltration BMPs are PROHIBITED in these areas; 3 This is only for the portion of flow that enters the infiltration basin; by-passed runoff does not receive treatment; 4 Low = < 30%; Medium = 30-65%; High = 65 -100%); 5 Assumes adequate pre-treatment

An infiltration trench is a shallow excavated trench that is backfilled with a coarse stone aggregate allowing for the temporary storage of runoff in the void space of the material in addition to the storage above the aggregate within the trench. For more information, see the following pages in this Manual.

• Overview for Infiltration trench
• Design criteria for Infiltration trench
• Construction specifications for Infiltration trench
• Operation and maintenance of Infiltration trench
• Cost-benefit considerations for Infiltration trench
• Calculating credits for infiltration trench
• External resources for Infiltration trench
• References for Infiltration trench
• Requirements, recommendations and information for using infiltration basin/underground infiltration BMPs in the MIDS calculator

Bioinfiltration basin

Bioinfiltration basin (Source: CDM Smith)</font size

Applications		Treatment capabilities2, 3, 4
Residential	yes	TSS	High5
Commercial	Yes	TN	Low/Medium5
Unltra-urban	Limited	TP	Medium/high6
Industrial	Yes1	Chloride	Low
Highway/road	Yes	Metals	High
Recreational	Yes	Oils and grease	High
		Pathogens	High
1 Unless the infiltration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. Infiltration BMPs are PROHIBITED in these areas; 2 This is only for the portion of flow that enters the infiltration basin; by-passed runoff does not receive treatment; 3 Low = < 30%; Medium = 30-65%; High = 65 -100%); 4 Assumes adequate pre-treatment; 5 This assumes no raised underdrain; 6 Certain soil mixes can actually leach P.

Bioinfiltration basins, often called rain gardens, use soil (typically engineered media or mixed soil) and native vegetation to capture runoff and remove pollutants. Both the media and underlying soil typically have high infiltration rates that allow captured water to infiltrate within a required drawdown time, usually 48 hours.