Green Infrastructure: Filtration practices can be an important tool for detention of stormwater runoff and treatment of pollutants in stormwater runoff. If the practice utilizes vegetation, additional benefits may include cleaner air, carbon sequestration, improved biological habitat, and aesthetic value.

Filtration practices treat stormwater by filtering pollutants. They are effective at attenuating suspended sediment and pollutants associated with that sediment. Most filtration practices utilize an underdrain and engineered soil media to attenuate pollutants and can be sized, in appropriate conditions, to treat the water quality volume. Some infiltration and/or loss of water through evapotranspiration occurs in most filtration practices. Filtration best management practices (BMPs) include, but are not limited, to

Raising an underdrain above the bottom of the filtration practice increases infiltration. However, the practice still functions as a filtration practice. For more information on practices with a raised underdrain, link here.

Biofiltration basin (bioretention with an underdrain)

photo of a bioretention BMP
Bioretention basin (Source: CDM Smith)
Applications and treatment capabilities for biofiltration basins
Applications Treatment capabilities2, 3
Residential Yes TSS High4
Commercial Yes TN Low/Medium
Ultra-urban Limited6 TP Medium/high5
Industrial Yes1 Chloride Low
Highway/road Yes Metals High
Recreational Yes Oils and grease High
Pathogens High
1 Unless the filtration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. 2 This is only for the portion of flow that enters the filtration basin; by-passed runoff does not receive treatment; 3 Low = < 30%; Medium = 30-65%; High = 65 -100%); 4 Assumes adequate pretreatment; 5 Certain soil mixes can leach P; 6 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

Biofiltration basins, often called rain gardens, use soil (typically engineered media or mixed soil) and native vegetation to capture runoff and remove pollutants. The media has a high infiltration rate but the underlying soil typically has a low infiltration rate (C or D soils). Therefore an underdrain is incorporated into the design. Water captured by the BMP is filtered through the engineered media and most of the treated water is captured by the underdrain and returned to the storm sewer system. Some water infiltrates below the underdrain and some water is taken up by plants. The amount of water that infiltrates can be maximized by raising the underdrain above the native soil or using an upturned elbow in the underdrain. Water captured by the BMP must drawdown within 48 hours. For more information, see the following pages in this Manual.

Permeable pavement (with an underdrain)

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 filtration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. 2 This is only for the portion of flow that enters the filtration basin; by-passed runoff does not receive treatment; 3 Low = < 30%; Medium = 30-65%; High = 65 -100%); 4 Assumes adequate pretreatment; 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 filtration 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 primarily to underdrains, though some infiltration occurs into the underlying soil. The amount of water that infiltrates can be maximized by raising the underdrain above the native soil or using an upturned elbow in the underdrain. Water captured by the BMP must drawdown within 48 hours. 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 (with an underdrain)

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 filtration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. 2 This is only for the portion of flow that enters the filtration basin; by-passed runoff does not receive treatment; 3 Low = < 30%; Medium = 30-65%; High = 65 -100%); 4 Assumes adequate pretreatment; 5 Certain soil mixes can leach P.

Source: see [1]

Tree trenches are a system of trees that are connected by an underground filtration 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. Water that is filtered through the engineered media largely passes to an underdrain and is returned to the storm sewer system. Some infiltration occurs into the underlying soil. The amount of water that infiltrates can be maximized by raising the underdrain above the native soil or using an upturned elbow in the underdrain. Water captured by the BMP must drawdown within 48 hours. 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. The drainage area to tree trenches and boxes 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 and stormwater step-pool (with check dams and underdrains)

dry swale photo
Dry swale (no check dams)
Applications and treatment capabilities for dry swale and step pools with check dams and underdrains
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 filtration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. 2 This is only for the portion of flow that enters the filtration basin; by-passed runoff does not receive treatment; 3 Low = < 30%; Medium = 30-65%; High = 65 -100%); 4 Assumes adequate pretreatment; 5 Certain soil mixes can leach P.

Source: see [2]

image of step pool
Stormwater step pool. Courtesy of Limnotech.

Similar to vegetated swales designed for stormwater conveyance, dry swales with underdrains are designed as linear, multi-celled stormwater filtration BMP’s. For high gradient conditions, stormwater step-pools can be utilized. By incorporating earthen or structural check dams, runoff is retained along a series of narrow, shallow basins or cells. This runoff is filtered through engineered media or soil and largely captured by an underdrain and returned to the storm sewer system. Some infiltration occurs into the underlying soil. The amount of water that infiltrates can be maximized by raising the underdrain above the native soil or using an upturned elbow in the underdrain. Water captured by the BMP must drawdown within 48 hours. 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 5 acres in size.

For information on dry swales, see the following pages.

For information on step pools, see the following pages.

Wet swales

wet swale photo
Wet swale (no check dams)
Applications and treatment capabilities for wet swale with check dams
Applications Treatment capabilities2, 3
Residential Yes TSS Medium4
Commercial Yes TN Low
Ultra-urban Limited TP Low5
Industrial Yes1 Metals Low
Highway/road Yes Oil and grease Low
Recreational Yes Pathogens Low
Chloride Low
1 Unless the filtration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. 2 This is only for the portion of flow that enters the filtration basin; by-passed runoff does not receive treatment; 3 Low = < 30%; Medium = 30-65%; High = 65 -100%); 4 Assumes adequate pretreatment; 5 Certain soil mixes can leach P.

Source: see [3]

Wet swales occur when the water table is located very close to the surface or water does not readily drain out of the swale. A wet swale acts as a very long and linear shallow biofiltration treatment system. The entire water quality treatment volume is stored within a series of cells created by check dams. Cells may be planted with emergent wetland plant species to improve pollutant removal. Wet swales are commonly used for drainage areas less than 5 acres in size.

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

Media (sand) filter

photo of an iron ehanced sand filter basin
Iron enhanced sand filter basin, Maplewood, MN. Photo courtesy of Barr Engineering.
Applications and treatment capabilities for media filters
Applications Treatment capabilities2, 3
Residential Yes TSS High4
Commercial Yes TN Medium
Ultra-urban Limited TP Medium
Industrial Yes1 Metals Medium
Highway/road Yes Oil and grease High
Recreational Yes Pathogens High
Chloride Low
1 Unless the filtration practice is located in an industrial area with exposed significant materials or from vehicle fuelling and maintenance areas. 2 This is only for the portion of flow that enters the filtration basin; by-passed runoff does not receive treatment; 3 Low = < 30%; Medium = 30-65%; High = 65 -100%); 4 Assumes adequate pretreatment.

Source: see [4]

Media filters treat stormwater through a variety of different filtering materials whose purpose is to remove pollution from runoff. Variants include surface sand filters, underground sand filters and perimeter sand filters. Most media filters have an underdrain and are effective at removing sediment and pollutants associated with sediment. Media filters may be enhanced with iron or other material to facilitate removal of dissolved pollutants, such as dissolved phosphorus. For more information on media filters, see the following sections in the Minnesota Stormwater Manual.

Green roofs

photo of green roof on the Target Center in Minneapolis, MN
Green roof on the Target Center in Minneapolis Minnesota. Note the vegetation free zones. Image Courtesy of The Kestrel Design Group, Inc.
Applications and treatment capabilities for wet swale with check dams
Applications Treatment capabilities1
Residential Yes TSS Medium
Commercial Yes TN Low
Ultra-urban Yes TP Low2
Industrial Yes Metals Low
Highway/road No Oil and grease Low
Recreational No Pathogens Low
Chloride Low
1 Low = < 30%; Medium = 30-65%; High = 65 -100%); 2 Certain soil mixes can leach P.

Green roofs typically occur at the beginning of stormwater treatment trains. Green roofs provide filtering of suspended solids and pollutants associated with those solids, although total suspended solid (TSS) concentrations from traditional roofs are generally low. Green roofs provide both volume and rate control, thus decreasing the stormwater volume being delivered to downstream Best Management Practices (BMPs).

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

Practices with a raised underdrain or internal water storage

image of biofiltration device with elevated underdrain
Biofiltration device with elevated underdrain
image of biofiltration device with internal water storage
Biofiltration device with internal water storage

A filtration practice with a raised underdrain provides a storage area below the invert of the underdrain discharge pipe. This area provides a recharge zone and quantity control can also be augmented with this storage area. The storage area is equal to the void space of the material used. Since the practice utilizes both infiltration and an underdrain, considerations include those for both infiltration practices and filtration with an underdrain at the bottom. These include an assessment of infiltration constraints and media.

A filtration practice with internal water storage is not commonly used in the Midwestern United States but is widely used in some places on the east coast, such as North Carolina. The use of an upturned elbow in this practice allows water to be retained within the practice, leading to increased pollutant removal, increased infiltration, and increased evapotranspiration. The practice is particularly effective at removing nitrogen through denitrification. The media should be 3 feet or more thick to allow water to be drawn down below the root zone. Underlying soils should be permeable enough to allow water stored within the practice to infiltrate. Hunt provides an overview of this practice.

Raising an underdrain or utilizing internal water storage enhances infiltration, but the practice still functions as a filtration practice. Pollutant removal for the infiltrated portion is 100 percent. We conducted simple calculations utilizing the Minimal Impact Design Standards (MIDS) calculator to illustrate the effect of a raised underdrain on volume and pollutant removal. The following inputs were used in the analysis.

  • Site zip code = 55155
  • 1 acre of impervious and 1 acre of pervious managed turf
  • Biofiltration with a raised underdrain, sized to hold the MIDS performance goal of 1.1 inches
  • Basin dimensions 3993 square feet by 1 foot ponding depth
  • Media Mix C (low phosphorus media)
  • 3 feet of media
  • Underlying soil = Hydrologic Soil Group C
  • Three scenarios
    • Underdrain at bottom
    • Underdrain raised 0.5 feet
    • Underdrain raised 0.8 feet (Note: this is the maximum depth below the underdrain to meet the 48 hour drawdown requirement)

Results of the analysis are summarized below.

  • Underdrain at bottom: 27% of performance goal achieved; 45% annual volume removal; 74% annual total phosphorus removed; 89% annual TSS removed
  • Underdrain raised 0.5 feet: 39% of performance goal achieved; 58% annual volume removal; 80% annual total phosphorus removed; 92% annual TSS removed
  • Underdrain raised 0.8 feet: 47% of performance goal achieved; 64% annual volume removal; 83% annual total phosphorus removed; 93% annual TSS removed

The analysis indicates significant increase in volume retained, moderate increase in phosphorus retention, and a small increase in TSS retention.

Unit processes for different filtration BMPs

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

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

Control Dry swale or step pool Wet swale Biofiltration Permeable pavement Tree box/tree trench Green roof
Peak flow attenuation X X X X X
Runoff volume reduction X X X X X
Infiltration X X X X
Dispersion X
Evapotranspiration X X X X X
Runoff collection and usage X X
Sedimentation X X X
Flotation X
Laminar separation
Swirl concentration
Sorption X X X X X
Precipitation X X
Coagulation X X
Filtration X X X X X X
Plant metabolism X X X
Nitrification/denitrification X X
Organic compound degradation X X X X X
Pathogen die off X
Temperature reduction X X X X X
Disinfection X X


Information tables

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

Overview table

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

Stormwater filtration BMPs - overview
Link to this table

Stormwater BMP General Overview Illustration
Dry swale or step pool Dry swales, sometimes called grass swales, are similar to bioretention cells but are configured as shallow, linear channels. Dry swales function primarily as a conveyance BMP but may incorporate check dams into the design, thus allowing water to be stored behind the check dam and filtered through the underlying soil or media. Discharge of filtered runoff occurs primarily through an underdrain, though some infiltration into the underlying soil occurs below the underdrain. image dry swale


step pool schematic
Wet swale Wet swales act as very long and linear shallow biofiltration or linear wetland treatment systems. Wet swales do not provide volume reduction and have limited treatment capability. Incorporation of check dams into the design allows treatment of a portion or all of the water quality volume within a series of cells created by the check dams. Screen shot of the Watershed tab for Wet swale
Biofiltration Basin Often called rain gardens, biofiltration basins use engineered or mixed soils and plantings to capture and filter runoff. Discharge of filtered runoff occurs primarily through an underdrain, though some infiltration into the underlying soil occurs below the underdrain.
Biofiltration 1 for credit page.jpg
Permeable pavement with underdrain Permeable pavements are paving surfaces that allow stormwater runoff to filter through surface voids into an underlying stone reservoir. 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 primarily through an underdrain, though some infiltration into the underlying soil occurs below the underdrain.
Permeable pavement icon.png
Tree Trench/Tree Box (with underdrain) A system of trees that are connected by an underground storage 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 filtered runoff occurs primarily through an underdrain, though some infiltration into the underlying soil occurs below the underdrain.
Symbol for tree trench with underdrain.jpg
Media filter (sand filter) Runoff is captured and stored in a filter media consisting of a sand filter bed (~18 inches), with temporary runoff storage above the bed. Pollutants are trapped or strained out at the surface of the filter bed. Discharge of filtered runoff occurs primarily through an underdrain.
schematic showing sand filter system
Green roof Green roofs consist of a a layer or layers of media that filter suspended solids and pollutants associated with those solids. Water passes through the media to an underlying impermeable layer that conveys the filtered water from the roof. green roof schematic

Contributing drainage area table

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

Contributing area is defined as the total area, including pervious and impervious surfaces, contributing to a BMP. It is assumed that in most cases, with the exception of green roofs and many permeable pavement systems, impervious surfaces will constitute more than 50 percent of the contributing area to the BMP and that most of this impervious is directly connected. The recommended contributing area to a BMP may be modified for the following conditions.

  • The recommended contributing area may be increased if pervious surfaces constitute the majority of the contributing area and soils are hydrologic soil group (HSG) A or B
  • The recommended contributing area should be decreased if impervious surfaces contribute more than 80 percent of the contributing area or if the entire impervious surface is directly connected and routed to the BMP
  • The recommended contributing area should be decreased or may be increased based on pollutant loading (decrease with higher pollutant loads)

Runoff coefficients may be calculated for an area contributing to a BMP. Runoff coefficients greater than about 0.55 are typical of urban areas having 50 percent or more impervious surface. Typical runoff coefficients are shown on these pages ([5], [6]) and discussed here. To see how runoff curve number is associated with impervious percentages, see Table 2-2a, page 17, at this link.

Stormwater filtration BMPs - contributing drainage area
Link to this table

Stormwater BMP Recommended contributing area Notes
Dry swale or step pool 5 acres or less A dry swale or step pool must be able to drawdown within 48-hours in order to preserve vegetation.
Wet swale 5 acres or less The boundary between upland and wetland type vegetation should be considered in the design. Different plant species will be tolerant of different periods of inundation.
Biofiltration Basin 5 acres or less Biofiltration 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 biofiltration 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.
Permeable Pavement (with underdrain) 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 (with underdrain) up to 0.25 acres per tree
Green roof Not applicable Contributing drainage from conventional roofs must be no larger than the surface area of the green roof

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 filtration BMPs - treatment properties
Link to this table

Stormwater BMP Illustration Pollutant Removal Mechanism Location in Treatment Train Pollutant Removal 1 Potential Application
Dry swale or step pool image dry swale


step pool schematic
Sedimentation / Infiltration Throughout
TSS: Medium
TN: Low
TP: Medium
Chloride: Low
Metals: Medium
Oils and Grease: Low
Pathogens: Low
Residential
Commercial
Industrial
Highway/Road
Recreational
Wet swale Screen shot of the Watershed tab for Wet swale Sedimentation / Transpiration Throughout
TSS: Medium
TN: Low
TP: Low
Chloride: Low
Metals: Low
Oils and Grease: Low
Pathogens: Low
Residential
Commercial
Industrial
Highway/Road
Recreation
Biofiltration Basin
Biofiltration 1 for credit page.jpg
Sedimentation / Filtration Beginning
TSS: High
TN: Low/Medium
TP: Medium/High2
Chloride: Low
Metals: High
Oils and Grease: High
Residential
Commercial
Retrofit
Permeable pavement with underdrain
Permeable pavement icon.png
Filtration Beginning
TSS: High
TN: Medium/High
TP: Medium/High
Chloride: Low
Metals: High
Oils and Grease: High
Residential
Commercial
Ultra Urban
Retrofit
Tree Trench/Tree Box (with underdrain)
Symbol for tree trench with underdrain.jpg
Filtration, Transpiration Throughout
TSS: High
TN: Medium/High
TP: Medium/High
Chloride: Low
Metals: High
Oils and Grease: High
Pathogens: High
Commercial
Ultra Urban
Retrofit
Media filter (sand filter)
schematic showing sand filter system
Filtration Throughout
TSS: High
TN: Medium
TP: Medium/High
Chloride: Low
Metals: Medium/High
Oils and Grease: High
Pathogens: High
Residential
Commercial
Industrial
Recreation
Green roof green roof schematic Filtration Throughout
TSS: High
TN: Low
TP: Low
Chloride: Low
Metals: High
Oils and Grease: High
Pathogens: High
Residential
Commercial
Ultra Urban
Industrial
Retrofit

12 Low = < 30%; Medium = 30‐65%; High = 65‐100%
2Some media mixes can leach phosphorus.

Selection considerations table

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

Stormwater filtration BMPs – selection considerations
Link to this Stormwater filtration BMPs – selection considerations

Stormwater BMP Illustration Cost Maintenance Requirements 3 Space needed Pretreatment 4 Habitat Quality 5
Dry swale or wet pool image dry swale


step pool schematic
Low to medium (depends on components) Simple‐Intensive Small Oil/Water Separator Sediment Basin (depending on watershed soil types, contributing drainage area, and potential for system fouling/plugging) Low
Wet pool Screen shot of the Watershed tab for Wet swale Low Simple Small Oil/Water Separator Low
Biofiltration Basin
Biofiltration 1 for credit page.jpg
Low $0.5‐$1.3 CF Simple‐Intensive Small to medium Needed Oil/Water Separator, Vegetated Filter, Sediment Basin, Water Quality Inlets Medium‐High
Permeable Pavement (with underdrain)
Permeable pavement icon.png
Medium 3‐10 CF Medium Small to medium No Pretreatment Required None
Tree Trench/Tree Box (with underdrain)
Tree trench icon.png
High

$1.80 ‐ $12.70 CF based on recommended soil volume

of 1,414 CF per tree
Intensive Small to large Needed Oil/Water Separator, Water Quality Inlets Medium
Media filter (sand filter)
schematic showing sand filter system
Low Simple-moderate Small Needed Oil/Water Separator, Vegetated Filter, Sediment Basin Low
Green roof green roof schematic High Moderate-intensive Small Low 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

Infiltration Summary Table

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

Related pages

The following practices typically employ an underdrain, which captures most of the runoff that enters the BMP. For information on these BMPs with no underdrain, see Stormwater infiltration Best Management Practices.

Other filtration BMPs, including pre-treatment practices

Manufactured devices

This page was last modified on 16 May 2018, at 09:51.

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