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General design criteria for iron-enhanced filtration systems includes | General design criteria for iron-enhanced filtration systems includes | ||
*water quality sizing for filtration applicable to iron-enhanced sand filters; | *water quality sizing for filtration applicable to iron-enhanced sand filters; | ||
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*head (top of filter to outlet invert) of 2 to 6 feet recommended depending upon application; and | *head (top of filter to outlet invert) of 2 to 6 feet recommended depending upon application; and | ||
− | {{alert| | + | {{alert|For projects covered under a Construction Stormwater permit, pretreatment is Required for sand filtration beds.|alert-danger}} |
+ | |||
+ | ==Design phase maintenance considerations== | ||
+ | {{alert|Maintenance considerations are an important component of design|alert-warning}} | ||
+ | |||
+ | Implicit in the design guidance is the fact that many design elements of infiltration and filtration systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include | ||
+ | *limiting drainage area; | ||
+ | *providing easy site access (''REQUIRED''); | ||
+ | *providing [[Glossary#P|pretreatment]] (''REQUIRED''); and | ||
+ | *utilizing native plantings (see [http://www.pca.state.mn.us/publications/manuals/stormwaterplants.html Plants for Stormwater Design]). NOTE this does not apply to the sand filter surface. | ||
+ | |||
+ | {{alert|The MPCA ''Recommends'' that the iron-sand filter surface be maintained free of vegetation or grasses. Ground cover can be used to stabilize the banks of the live storage zone above the elevation of the sand filter surface. Shrubs or other woody plants can be planted above live storage.|alert-warning}} | ||
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+ | For more information on design information for individual infiltration and filtration practices, [http://stormwater.pca.state.mn.us/index.php/Category:Design_criteria link here]. | ||
==Design elements== | ==Design elements== | ||
===Physical feasibility initial check=== | ===Physical feasibility initial check=== | ||
Before deciding to use an iron-enhanced sand filter for stormwater management, the designer should consider several items that affect the feasibility of using such a practice at a given location. The following list of considerations will help in making an initial judgment as to whether a filtration device is the appropriate BMP for the site. | Before deciding to use an iron-enhanced sand filter for stormwater management, the designer should consider several items that affect the feasibility of using such a practice at a given location. The following list of considerations will help in making an initial judgment as to whether a filtration device is the appropriate BMP for the site. | ||
− | *Drainage area: In addition to the practical size limitations of constructing a properly functioning (e.g., designing a filter than can drain properly and can be accessed for maintenance) iron-enhanced sand filter basin or sand bench in wet ponds, treatment objectives and credit needs will determine the drainage area that can be treated. Runoff volume is a function of soil type and watershed imperviousness. Given space availability or other factors that will dictate filter treatment volume capacity (V<sub>t</sub>). | + | *Drainage area: In addition to the practical size limitations of constructing a properly functioning (e.g., designing a filter than can drain properly and can be accessed for maintenance) iron-enhanced sand filter basin or sand bench in wet ponds, treatment objectives and credit needs will determine the drainage area that can be treated. Runoff volume is a function of soil type and watershed imperviousness. Given space availability or other factors that will dictate filter treatment volume capacity (V<sub>t</sub>). For more information on contributing area, see [[Contributing drainage area to stormwater BMPs]]. |
*Site topography and slopes: Sloped areas immediately adjacent to practice are ''Recommended'' to be less than 20 percent but greater than 1 percent, to promote positive flow towards the practice. Iron-enhanced sand filters do not require any slope to promote treatment. | *Site topography and slopes: Sloped areas immediately adjacent to practice are ''Recommended'' to be less than 20 percent but greater than 1 percent, to promote positive flow towards the practice. Iron-enhanced sand filters do not require any slope to promote treatment. | ||
*Soils: No restrictions or sizing adjustments are required by soil type. | *Soils: No restrictions or sizing adjustments are required by soil type. | ||
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*Use of permeable filter fabric around the drain pipe or between media layers is ''Not Recommended'' as the filter fabric may clog, reduce infiltration into the drain pipe, or limit aeration of the filter media. | *Use of permeable filter fabric around the drain pipe or between media layers is ''Not Recommended'' as the filter fabric may clog, reduce infiltration into the drain pipe, or limit aeration of the filter media. | ||
− | === | + | ===Pretreatment=== |
− | The | + | The pretreatment requirements for media filters apply to iron-enhanced sand filter basins. Pretreatment is provided by the wet ponds associated with iron-enhanced sand filter benches. |
===Treatment=== | ===Treatment=== | ||
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===Iron-enhanced sand filtration basins=== | ===Iron-enhanced sand filtration basins=== | ||
[[File:Beam Ave sand filter 1.jpg|left|thumb|300px|alt=photo of an iron ehanced sand filter basin|<font size=3>Iron enhanced sand filter basin, Maplewood, MN. Photo courtesy of Barr Engineering.</font size>]] | [[File:Beam Ave sand filter 1.jpg|left|thumb|300px|alt=photo of an iron ehanced sand filter basin|<font size=3>Iron enhanced sand filter basin, Maplewood, MN. Photo courtesy of Barr Engineering.</font size>]] | ||
− | [[File:iron enhanced sand filter basin schematic 1.jpg|thumb|300px|alt=schematic of an iron enhanced sand filter basin|<font size=3>Iron-enhanced sand filter basin schematic | + | [[File:iron enhanced sand filter basin schematic 1.jpg|thumb|300px|alt=schematic of an iron enhanced sand filter basin|<font size=3>Iron-enhanced sand filter basin schematic.</font size>]] |
Iron-enhanced sand filtration basins are analogous to [[Filtration|media filters]]. The basic design elements of an iron-enhanced sand filter basin include: | Iron-enhanced sand filtration basins are analogous to [[Filtration|media filters]]. The basic design elements of an iron-enhanced sand filter basin include: | ||
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===Iron-enhanced sand filtration bench in wet ponds=== | ===Iron-enhanced sand filtration bench in wet ponds=== | ||
[[File:iron enhanced sand bench Prior Lake 1.jpg|left|thumb|300px|alt=photo of an iron ehanced sand bench|<font size=3>Iron enhanced sand bench, Prior Lake, MN. Photo courtesy of Ross Bintner.</font size>]] | [[File:iron enhanced sand bench Prior Lake 1.jpg|left|thumb|300px|alt=photo of an iron ehanced sand bench|<font size=3>Iron enhanced sand bench, Prior Lake, MN. Photo courtesy of Ross Bintner.</font size>]] | ||
− | [[File:iron enhanced sand filter bench schematic 1.jpg|thumb|300px|alt=schematic of an iron enhanced sand filter bench|<font size=3>Iron-enhanced sand filter bench schematic | + | [[File:iron enhanced sand filter bench schematic 1.jpg|thumb|300px|alt=schematic of an iron enhanced sand filter bench|<font size=3>Iron-enhanced sand filter bench schematic.</font size>]] |
An iron-enhanced sand filtration bench in a wet pond is essentially a [[Types of stormwater ponds#Extended wet detention basin|wet extended detention pond]] with a permanent pool and a flood pool. The outlet structure of the pond is designed such that the water in the flood pool during and after a storm event is held above the elevation of the iron-enhanced sand filter bench, thereby allowing water to filter through the bench. The basic design elements of an iron-enhanced sand filter basin include: | An iron-enhanced sand filtration bench in a wet pond is essentially a [[Types of stormwater ponds#Extended wet detention basin|wet extended detention pond]] with a permanent pool and a flood pool. The outlet structure of the pond is designed such that the water in the flood pool during and after a storm event is held above the elevation of the iron-enhanced sand filter bench, thereby allowing water to filter through the bench. The basic design elements of an iron-enhanced sand filter basin include: |
General design criteria for iron-enhanced filtration systems includes
Implicit in the design guidance is the fact that many design elements of infiltration and filtration systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include
For more information on design information for individual infiltration and filtration practices, link here.
Before deciding to use an iron-enhanced sand filter for stormwater management, the designer should consider several items that affect the feasibility of using such a practice at a given location. The following list of considerations will help in making an initial judgment as to whether a filtration device is the appropriate BMP for the site.
Conveyance design elements for filtration are largely applicable to iron-enhanced filtration with the following exceptions:
The pretreatment requirements for media filters apply to iron-enhanced sand filter basins. Pretreatment is provided by the wet ponds associated with iron-enhanced sand filter benches.
The treatment guidelines applicable to filtration are also applicable to iron-enhanced filtration.
The MPCA Recommends that the iron-sand filter surface be maintained free of vegetation or grasses. Ground cover can be used to stabilize the banks of the live storage zone above the elevation of the sand filter surface. Shrubs or other woody plants can be planted above live storage.
Iron-enhanced sand filtration basins are analogous to media filters. The basic design elements of an iron-enhanced sand filter basin include:
An iron-enhanced sand filtration bench in a wet pond is essentially a wet extended detention pond with a permanent pool and a flood pool. The outlet structure of the pond is designed such that the water in the flood pool during and after a storm event is held above the elevation of the iron-enhanced sand filter bench, thereby allowing water to filter through the bench. The basic design elements of an iron-enhanced sand filter basin include: