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

  • infiltration basins,
  • infiltration trenches (includes dry wells),
  • underground infiltration systems,
  • bioinfiltration,
  • permeable pavements,
  • tree trenches and tree boxes, and
  • dry swale with check dams.

These are discussed briefly below. Additional information about these BMPs can be found in the following tables.

Infiltration basin

photo of an infiltration basin
Photo of an infiltration basin. Source: Clark County, Washington, with permission.
Applications and treatment capabilities for infiltration basins
Applications Treatment capabilities3, 4, 5
Residential Yes TSS High6
Commercial Yes TN Medium/high
Ultra-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 fueling and maintenance areas. Infiltration BMPs are PROHIBITED in these areas; 3Underground infiltration systems may have different (likely lower) pollutant removal capabilities than what is provided in this table. These systems may have a wider application range. 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

Sources: Schueler, 1987, 1992; USEPA 1993a, 1993b; Maniquiz et al., 2010; NPRPD, 2007; California Stormwater Manual, 2009; Pennsylvania Stormwater Manual, 2006

An infiltration basin is a natural or constructed impoundment that captures, temporarily stores and infiltrates the design volume of water. Drawdown of this stored runoff occurs through infiltration into the surrounding naturally permeable soil. The required drawdown time is 48 hours or less. Water that is stored but not infiltrated must leave the BMP, typically through an outlet, within the required drawdown time. In the case of a constructed basin, the impoundment is created by excavation or embankment. Infiltration basins are commonly used for drainage areas of 5 to 50 acres with land slopes that are less than 20 percent. Typical depths range from 2 to 6 feet, including bounce in the basin. The sizing is to control stormwater volumes at the regional or development scale as opposed to bioretention basins (rain gardens) that are designed at the site scale. Typical dimensions range from 1,000 square feet up to an acre. Infiltration basins are commonly constructed with plant species that can tolerate and thrive in this unique growing environment.

For more information, see the following pages in this Manual.

Infiltration trench

Photo of a Infiltration trench in Lino Lakes
Photo of a Infiltration trench in Lino Lakes
Applications and treatment capabilities for infiltration trenches, dry well, underground infiltration
Applications Treatment capabilities3, 4
Residential Yes TSS5 High5
Commercial Yes TN Medium/high
Ultra-urban Yes TP Medium/high
Industrial Yes1 Chloride Low
Highway/road 2 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 Yes for infiltration trench, limited for underground infiltration, no for dry well; 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

Sources: Schueler, 1987, 1992; USEPA 1993a, 1993b; Maniquiz et al., 2010; NPRPD, 2007; California Stormwater Manual, 2009; Pennsylvania Stormwater Manual, 2006

An infiltration trench is a shallow excavated trench, typically 3 to 6 feet deep, that is backfilled with a coarse stone aggregate allowing for the temporary storage of runoff in the void space of the material. Drawdown of this stored runoff occurs through infiltration into the surrounding naturally permeable soil. Infiltration trenches may be modified to become stormwater tree trenches and boxes where applicable with the addition of growing medium. All water captured by the BMP must be removed within 48 hours through infiltration and/or a drain. Trenches are commonly used for drainage areas less than 5 acres in size.

Caution: To avoid an infiltration trench being classified as a Class V injection well, it is strongly recommended that the length of the trench be at least 2 times greater than the depth of the trench.

For more information, see the following pages in this Manual.

Dry wells (a.k.a. infiltration tubes, french drains, soak-away pits or soak holes)

A dry well or soak away pit is a smaller variation of an infiltration trench. It is a subsurface storage facility (a structural chamber or an excavated pit backfilled with a coarse stone aggregate) that receives and temporarily stores stormwater runoff. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil. Due to their size, dry wells are typically designed to handle stormwater runoff from smaller drainage areas, less than one acre in size (e.g. roof tops).

Underground infiltration systems

Several underground infiltration systems, including pre-manufactured pipes, vaults, and modular structures, have been developed as alternatives to infiltration basins and trenches for space-limited sites and stormwater retrofit applications. Underground infiltration systems are occasionally the only stormwater BMP options on fully developed sites as they can be located under other land uses such as parking lots or play areas. These systems are similar to infiltration basins and trenches in that they are designed to capture, temporarily store and infiltrate the design volume of stormwater over several days. Underground infiltration systems are generally applicable to small development sites (typically less than 10 acres) and should be installed in areas that are easily accessible to routine and non-routine maintenance. These systems should not be located in areas or below structures that cannot be excavated in the event that the system needs to be replaced or invasive maintenance is required to maintain performance.

Bioinfiltration basin

photo of a bioinfiltration BMP
Bioinfiltration basin (Source: CDM Smith)
Applications and treatment capabilities for bioinfiltration basins
Applications Treatment capabilities2, 3
Residential Yes TSS High4
Commercial Yes TN Low/Medium5
Ultra-urban Limited7 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 underdrain; 6 Certain soil mixes can leach P; 7 Due to a size restriction

Sources: EPA Factsheet, 1999; Davis et al., 2001, 2003, 2006; Hsieh and Davis, 2005; Hong et al., 2006; Hunt et al., 2006; NPRPD, 2007; Li and Davis, 2009; Diblasi et al., 2009; Passeport et al., 2009; Brown et at., 2011a, b; Komlos et al., 2012; Denich et al., 2013; Li and Davis, 2013; California Stormwater BMP

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. For more information, see the following pages in this Manual.

Permeable pavement

photo of permeable pavement
Permeable pavement (Source: CDM Smith)
Applications and treatment capabilities for permeable pavement
Applications Treatment capabilities2, 3
Residential Yes TSS High4
Commercial Yes TN Medium/High
Ultra-urban Yes Nitrate Low/Medium
Industrial Yes1 TP Medium/High
Retrofit Yes Chloride Low
Highway/road Yes Metals High
Recreational Yes Oils and grease High
Pathogens 5
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 Insufficient information

Source: Schueler, 1987; Pratt et al, 1999; Adams, 2003; Brattebo and Booth, 2003; Adams, 2003; Bean et al, 2007; SEMCOG, 2008; International Stormwater Database, 2012

Permeable pavements are paving surfaces that allow stormwater runoff to filter through surface voids into an underlying stone reservoir for infiltration and/or storage. They are suitable for driveways, trails, parking lots, and roadways with lighter traffic. The most commonly used permeable pavement surfaces are pervious concrete, porous asphalt, and permeable interlocking concrete pavers (PICP). All permeable pavements have a similar design layering system, consisting of a surface pavement layer, an underlying stone aggregate reservoir layer, optional underdrains for filtration and geotextile over non-compacted soil subgrade. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil. The drainage area leading to permeable pavements should not exceed twice the surface area of the final pavement surface.

For more information, see the following pages in this Manual.

Tree box/Tree trench

photo of tree box
Tree box (Source: CDM Smith)
Applications and treatment capabilities for tree box/tree trench
Applications Treatment capabilities2, 3
Residential Yes TSS High4
Commercial Yes TN Low/Medium
Ultra-urban Yes TP Medium/High5
Industrial Yes1 Chloride Low
Highway/road No 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 Certain soil mixes can leach P.

Source: see [1]

Tree trenches are a system of trees that are connected by an underground infiltration structure. The system consists of a stormwater tree trench or box lined with geotextile fabric with structural stone, gravel or soil boxes in which the trees are placed. Tree systems consist of an engineered soil or rock layer designed to treat stormwater runoff via filtration through plant and soil/rock media, and through evapotranspiration from trees. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil. Tree species are carefully selected to survive both inundation and drought conditions in urban environments where they will be potentially affected by chloride and other traffic concerns. Tree trenches and boxes drainage areas should be less than five acres depending on the size of each trench. Irrigation, whether manual or automated, is strongly encouraged during the tree’s establishment period.

For more information, see the following pages in this Manual.

Trees - general
Tree boxes/tree trenches

Dry swale with check dams

Applications and treatment capabilities for dry swale with check dams
Applications Treatment capabilities2, 3
Residential Yes TSS High4
Commercial Yes TN Low/Medium
Ultra-urban Limited TP Low/Medium5
Industrial Yes1 Chloride Low
Highway/road Yes Metals High
Recreational Yes Oils and grease High
Pathogens Medium
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 Certain soil mixes can leach P.

Source: see [2]

Similar to vegetated swales designed for stormwater conveyance, dry swales with check dams are designed as linear, multi-celled stormwater infiltration BMP’s. By incorporating earthen or structural check dams, runoff is retained and infiltrated along a series of narrow, shallow basins or cells. Coarse vegetation such as decorative plantings or even turf grass slow runoff movement. This system is designed to move, store, and infiltrate runoff from impervious surfaces such as linear roadways or parking lots. Dry swales are best designed for sites under one acre in size.

Enhanced turf

Infiltration can be enhanced on soils that have been improved or amended. This manual contains limited information on enhanced turf and does not provide guidance for design, construction, maintenance, and assessment of enhanced turf. Information on use of compost in soil and credits associated with improved turf can be found on the Turf page. A discussion of alleviating compaction from construction activities can be found here.

Warning: Enhanced turf cannot be used to meet requirements of the Construction Stormwater General permit because infiltrated water does not represent an instantaneous volume.

Unit processes for different infiltration BMPs

The following table provides a summary of unit processes for the different infiltration BMPs.

Unit processes of stormwater treatment techniques (Adapted from WEF, 2008)
Link to this table

Control Infiltration basin Infiltration trench Bioinfiltration Permeable pavement Tree box/tree trench Enhanced turf
Peak flow attenuation X X X X
Runoff volume reduction X X X X X
Infiltration X X X X X X
Dispersion
Evapotranspiration X X
Runoff collection and usage X1 X1
Sedimentation X X X
Flotation X X
Laminar separation
Swirl concentration
Sorption X X X X
Precipitation X X X X
Coagulation X X X X
Filtration X
Plant metabolism X X X
Nitrification/denitrification X X X
Organic compound degradation X X X X
Pathogen die off X X X
Temperature reduction X X X X
Disinfection X X X X

1 If underdrain is present


Information tables

The following tables describe and differentiate different characteristics of stormwater infiltration BMPs.

Overview table

The following table provides a brief description and schematic of each stormwater infiltration BMP.

Stormwater infiltration BMPs - overview
Link to this table

Stormwater BMP General Overview Illustration
Infiltration Basin A natural or constructed impoundment that captures, temporarily stores and infiltrates the design volume of water into the surrounding naturally permeable soil over several days. In the case of a constructed basin, the impoundment is created by excavation or embankment.
Infiltration basin icon.png
Bioinfiltration Basin Often called rain gardens, bioinfiltration basins use engineered or mixed soils and plantings to capture and infiltrate runoff. Pollutants are removed using highly permeable soils that are able to draw the basin down in less than 48 hours.
Bioinfiltration icon.png
Infiltration Trench Synonym: Infiltration Gallery 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. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil.
Infiltration trench icon.png
Dry Well Synonym: Infiltration Tube, French Drain, Soak‐Away Pits, Soak Holes A smaller variation of an infiltration trench. It is a subsurface storage facility (a structural chamber or an excavated pit backfilled with a coarse stone aggregate) that receives and temporarily stores stormwater runoff. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil. Due to their size, dry wells are typically designed to handle stormwater runoff from smaller drainage areas.
Dry well icon.png
Underground Infiltration Several underground infiltration systems, including pre‐manufactured pipes, vaults, and modular structures, have been developed as alternatives to infiltration basins and trenches for space‐limited sites and stormwater retrofit applications. These systems are similar to infiltration basins and trenches in that they are designed to capture, temporarily store and infiltrate the design volume of stormwater over several days. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil.
Underground infiltration icon.png
Dry Swale with Check Dams Similar to vegetated swales designed for stormwater conveyance, dry swales with check dams are designed as linear, multi‐celled stormwater infiltration BMPs. By incorporating earthen, structural or rock check dams, runoff is retained and infiltrated along a series of narrow, shallow basins or cells. Coarse vegetation such as decorative plantings or even turf grass slow runoff movement. This system is designed to move, store, and infiltrate runoff from impervious surfaces such as linear roadways or parking lots.
Swale check icon.png
Permeable Pavement Permeable pavements are paving surfaces that allow stormwater runoff to filter through surface voids into an underlying stone reservoir for infiltration and/or storage. The most commonly used permeable pavement surfaces are pervious concrete, porous asphalt, and permeable interlocking concrete pavers (PICP). All permeable pavements have a similar structure, consisting of a surface pavement layer, an underlying stone aggregate reservoir layer, optional underdrains and geotextile over uncompacted soil subgrade. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil.
Permeable pavement icon.png
Tree Trench/Tree Box A system of trees that are connected by an underground infiltration structure. The system consists of a trench lined with geotextile fabric with structural stone, gravel or soil boxes in which the trees are placed. Tree systems consist of an engineered soil layer designed to treat stormwater runoff via filtration through plant and soil media, and through evapotranspiration from trees. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil.
Tree trench icon.png


Contributing drainage area table

The following table provides a summary of recommended contributing drainage area for each stormwater infiltration BMP.

Stormwater infiltration BMPs - contributing drainage area
Link to this table

Stormwater BMP Recommended contributing area Notes
Infiltration Basin 50 acres or less A natural or constructed impoundment that captures, temporarily stores and infiltrates the design volume of water into the surrounding naturally permeable soil over several days. In the case of a constructed basin, the impoundment is created by excavation or embankment.
Bioinfiltration Basin 5 acres or less Bioinfiltration basins must meet the required 48 hour drawdown time and must be sized in order to allow for adequate maintenance. It is HIGHLY RECOMMENDED that bioinfiltration basins be designed to prevent high levels of bounce as submerging vegetation may inhibit plant growth. A maximum wet storage depth of 1.5 feet is HIGHLY RECOMMENDED.
Infiltration Trench 5 acres or less
Dry Well Synonym: Infiltration Tube, French Drain, Soak‐Away Pits, Soak Holes 1 acre or less (rooftop only)
Underground Infiltration 10 acres or less Though feasible, larger underground infiltration systems may cause groundwater contamination as water is not able to infiltrate through a surface cover. In addition, wind flocculation, UV degradation, and bacterial degradation, which provide additional treatment in surface systems, do not occur in underground systems. Because performance research is lacking for larger features, it is HIGHLY RECOMMENDED that the contributing drainage area to a single device not exceed 10 acres.
Dry Swale with Check Dams 5 acres or less
Permeable Pavement It is RECOMMENDED that external contributing drainage area not exceed the surface area of the permeable pavement. It is HIGHLY RECOMMENDED that external contributing drainage area not exceed twice the surface area of the permeable pavement It is RECOMMENDED that external drainage area be as close to 100% impervious as possible. Field experience has shown that drainage area (pervious or impervious) can contribute particulates to the permeable pavement and lead to clogging. Therefore, sediment source control and/or pretreatment should be used to control sediment run-on to the permeable pavement section.
Tree Trench/Tree Box up to 0.25 acres per tree

References: Virginia, North Carolina, West Virginia, Maine, Lake Tahoe, Connecticut, Massachusetts, New York, Wisconsin, Vermont, New Hampshire, Ontario, Pennsylvania


Treatment properties table

The following table provides information on pollutant removal mechanism(s), location in the stormwater treatment train, general pollutant removal, and potential applications for each of the stormwater BMPs.

Stormwater infiltration BMPs - treatment properties
Link to this table

Stormwater BMP Illustration Pollutant Removal Mechanism Location in Treatment Train Pollutant Removal 1,2 Potential Application 1
Infiltration Basin
Infiltration basin icon.png
Sedimentation / Infiltration End TSS: High

TN: Medium/High TP: Medium/High Chloride: Low Metals: High Oils and Grease: High

Pathogens: High
Residential: Yes

Commercial: Yes Ultra Urban: Limited Industrial: Limited Retrofit: Yes

Highway/Road: Limited
Bioinfiltration Basin
Bioinfiltration icon.png
Sedimentation / Infiltration Beginning TSS: High

TN: Low/Medium TP: Medium/High Chloride: Low Metals: High

Oils and Grease: High
Residential: Yes

Commercial: Yes Ultra Urban: Limited Industrial: Limited Retrofit: Yes

Highway/Road: Limited
Infiltration Trench
Synonym: Infiltration Gallery
Infiltration trench icon.png
Infiltration nd TSS: High

TN: Medium/High TP: Medium/High Chloride: Low Metals: High Oils and Grease: High

Pathogens: High
Residential: Yes

Commercial: Yes Ultra Urban: Yes Industrial: Limited Retrofit: Yes

Highway/Road: Yes
Dry Well
Synonym: Infiltration Tube, French Drain, Soak‐Away Pits, Soak Holes
Dry well icon.png
Infiltration throughout TSS: High

TN: Medium/High TP: Medium/High Chloride: Low Metals: High Oils and Grease: High

Pathogens: High
Residential: Yes

Commercial: Yes Ultra Urban: Yes Industrial: Limited Retrofit: Yes

Highway/Road: No
Underground Infiltration
Underground infiltration icon.png
Sedimentation / Infiltration / Flotation/Skimming End TSS: High

TN: Medium/High TP: Medium/High Chloride: Low Metals: High Oils and Grease: High

Pathogens: High
Residential: Yes

Commercial: Yes Ultra Urban: Yes Industrial: Limited Retrofit: Yes

Highway/Road: Limited
Dry Swale with Check Dams
Swale check icon.png
Sedimentation / Infiltration Throughout TSS: High

TN: Low/Medium TP: Low/Medium Chloride: Low Metals: High Oils and Grease: High

Pathogens: Medium
Residential: Yes

Commercial: Yes Ultra Urban: Limited Industrial: Yes Retrofit: Limited

Highway/Road: Yes
Permeable Pavement
Permeable pavement icon.png
Infiltration Beginning TSS: High

TN: Medium/High TP: Medium/High Chloride: Low Metals: High

Oils and Grease: High
Residential: Yes

Commercial: Yes Ultra Urban: Yes Industrial: Limited Retrofit: Yes

Highway/Road: Limited
Tree Trench/Tree Box
Tree trench icon.png
Infiltration, Transpiration Throughout TSS: High

TN: Medium/High TP: Medium/High Chloride: Low Metals: High Oils and Grease: High

Pathogens: High
Residential: Limited

Commercial: Yes Ultra Urban: Yes Industrial: Limited Retrofit: Yes

Highway/Road: Limited

1 Treatment Capabilities and Potential Applications referenced from Manual Section BMP's for stormwater infiltration
2 Low = < 30%; Medium = 30‐65%; High = 65‐100%


Selection considerations table

The following table provides information on general cost, maintenance requirements, pretreatment needs, and habitat quality for each of the stormwater infiltration BMPs.

Stormwater infiltration BMPs – selection considerations
Link to this table

Stormwater BMP Illustration Cost Maintenance Requirements 3 Pre‐treatment 4 Habitat Quality 5
Infiltration Basin
Infiltration basin icon.png
Low $0.5‐$1.3 CF Simple‐Intensive Needed Oil/Water Separator, Vegetated Filter, Sediment Basin, Water Quality Inlets Low
Bioinfiltration Basin
Bioinfiltration icon.png
Low $0.5‐$1.3 CF Simple‐Intensive Needed Oil/Water Separator, Vegetated Filter, Sediment Basin, Water Quality Inlets Medium‐High
Infiltration Trench Synonym: Infiltration Gallery
Infiltration trench icon.png
Low $1‐$4 CF Medium Needed

Oil/Water Separator, Vegetated Filter, Sediment

Basin, Water Quality Inlets
None
Dry Well Synonym: Infiltration Tube, French Drain, Soak‐Away Pits, Soak Holes
Dry well icon.png
Low $1‐$4 CF Medium Needed

Oil/Water Separator, Vegetated Filter, Water

Quality Inlets
None
Underground Infiltration
Underground infiltration icon.png
High 14 CF Medium Needed Oil/Water Separator, Water Quality Inlets None
Dry Swale with Check Dams
Swale check icon.png
Low $.5‐$1.3 CF Simple‐Medium Needed Vegetated Filter, Water Quality Inlets Low‐Medium
Permeable Pavement
Permeable pavement icon.png
Medium 3‐10 CF Medium No Pretreatment Required None
Tree Trench/Tree Box
Tree trench icon.png
High

$1.80 ‐ $12.70 CF based on recommended soil volume

of 1,414 CF per tree
Intensive Needed Oil/Water Separator, Water Quality Inlets Medium

1 Maintenance requirements to be addressed and updated in future section
2 Pretreatment requirements to be revised as per updated section
3 Habitat quality refers to the possible diversity of plantings commonly installed with each BMP


See Infiltration Summary Table

To see all information contained in the previous tables in a single table, click on the following link: Infiltration Summary Table

Related pages