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==Design Variants==
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#REDIRECT [[BMPs for stormwater infiltration]]
===Infiltration Basin===
 
<p>An infiltration [[Glossary#B|basin]] is a natural or constructed impoundment that captures, temporarily stores and [[Glossary#I|infiltrates]] the design volume of water over several days. 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 12 feet, including bounce in the basin. An [[Glossary#I|infiltrates]] [[Glossary#B|basin]] construction detail is located in the [[Computer-aided design and drafting (CAD/CADD) drawings]] section.</p>
 
  
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{{alert|This section on infiltration trench includes information for infiltration trench and infiltration basin. We anticipate reorganizing this section and eventually having individual sections for infiltration trench, infiltration basin, and bioretention-bioinfiltration|alert-info}}
  
{{:Infiltration Trench - Construction inspection checklist}}
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==Infiltration basin==
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An infiltration [[Glossary#B|basin]] is a natural or constructed impoundment that captures, temporarily stores and [[Glossary#I|infiltrates]] the design volume of water over several days. 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 12 feet, including bounce in the basin. An infiltrates basin construction detail is located in the [[CADD images for individual best management practices|drawings]] section.
  
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==Infiltration trench (a.k.a. infiltration gallery)==
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An infiltration trench is a shallow excavated trench, typically 3 to 12 feet deep, 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. Trenches are commonly used for drainage areas less than 5 acres in size.
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{{alert|To avoid an infiltration trench being classified as a [[Glossary#C|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.|alert-danger}}
  
===Infiltration Trench (a.k.a. infiltration gallery)===
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==Dry wells (a.k.a. infiltration tubes, french drains, soak-away pits or soak holes)==
<p>An [[Glossary#I|infiltration]] trench is a shallow excavated trench, typically 3 to 12 feet deep, that is backfilled with a coarse stone aggregate allowing for the temporary storage of [[Glossary#|runoff]] in the void space of the material. Discharge of this stored [[Glossary#|runoff]] occurs through [[Glossary#I|infiltration]] into the surrounding naturally permeable soil. Trenches are commonly used for drainage areas less than 5 acres in size.</p>
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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 [[Glossary#R|runoff]] from smaller drainage areas, less than one acre in size (e.g. roof tops).
  
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==Underground infiltration systems==
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Several underground infiltration systems, including pre-manufactured pipes, vaults, and modular structures, have been developed as alternatives to infiltration [[Glossary#B|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. 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.
  
===Dry Wells (a.k.a. [[Glossary#I|infiltration]] tubes, french drains, soak-away pits or soak holes)===
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<noinclude>
<p>A dry well or soak away pit is a smaller variation of an [[Glossary#I|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 [[Glossary#R|runoff]]. Discharge of this stored runoff occurs through [[Glossary#I|infiltration]] into the surrounding naturally permeable soil. Due to their size, dry wells are typically designed to handle stormwater [[Glossary#R|runoff]] from smaller drainage areas, less than one acre in size (e.g. roof tops). </p>
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==Related pages==
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*[[Overview for Infiltration trench]]
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*[[Types of Infiltration trench]]
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*[[Design criteria for Infiltration trench]]
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*[[Construction specifications for Infiltration trench]]  
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*[[Operation and maintenance of Infiltration trench]]
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*[[Assessing the performance of infiltration trenches and basins]]
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*[[Cost-benefit considerations for Infiltration trench]]
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*[[External resources for Infiltration trench ]]
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*[[References for infiltration]]
  
 
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[[Category:Level 3 - Best management practices/Guidance and information/BMP types and terminology]]
===Underground Infiltration Systems===
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[[Category:Level 3 - Best management practices/Structural practices/Infiltration (trench/basin)]]
<p>Several underground [[Glossary#I|infiltration]] systems, including pre-manufactured pipes, vaults, and modular structures, have been developed as alternatives to infiltration [[Glossary#B|basins]] and trenches for space-limited sites and stormwater retrofit applications. These systems are similar to [[Glossary#I|infiltration]] [[Glossary#B|basins]] and trenches in that they are designed to capture, temporarily store and infiltrate the design volume of stormwater over several days. Underground [[Glossary#I|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. </p>
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</noinclude>
 
 
 
 
===Retrofit Suitability===
 
<p>The narrow and versatile shape of infiltration trenches and dry wells makes them well suited for retrofit projects. For example, [[Glossary#I|infiltration]] practices can be situated along the margin or perimeter of a developed site or roadway in many cases. They are particularly desirable as retrofit practices in [[Glossary#W|watersheds]] or catchments that are targeting volume reduction practices to help minimize channel [[Glossary#E|erosion]]. {{alert|Use of [[Glossary#I|infiltration]] practices is ''PROHIBITED'' in the [http://www.pca.state.mn.us/index.php/water/water-types-and-programs/stormwater/construction-stormwater/index.html CGP] for treatment of [[Glossary#R|runoff]] from industrial areas with exposed significant materials or from vehicle fueling and maintenance areas.|alert-danger}} Generally, [[Glossary#I|infiltration]] should not be used to treat [[Glossary#R|runoff]] from manufacturing or industrial sites or other areas with high pollutant concentrations unless correspondingly high levels of [[Glossary#P|pretreatment]] are provided.</p>
 
 
 
 
 
===Special Receiving Waters Suitability===
 
<p>The [[Glossary#B|BMP]] design restrictions for special watersheds table below provides guidance regarding the use of [[Glossary#I|infiltration]] practices in areas upstream of special [[Glossary#R|receiving waters]]. This table is an abbreviated version of a larger table in which other [[Glossary#B|BMP]] groups are similarly evaluated. The corresponding information about other [[Glossary#B|BMPs]] is presented in the respective sections of this Manual.</p>
 
 
 
 
 
{{:BMP design restrictions for special watersheds}}
 
 
 
 
 
===Cold Climate Suitability===
 
<p>Various options for use of [[Glossary#I|infiltration]] are available for treating snowmelt runoff. Some of the installations are built below the frost line (trenches, sub-grade proprietary chambers) and do not need further adaptation for the cold. However, some special consideration as described in the [[Cold climate impact on runoff management]] section is ''HIGHLY RECOMMENDED'' for surface systems. The problem with [[Glossary#I|infiltration]] in cold weather is the ice that forms both over the top of the facility and within the soil interstices. To avoid these problems to the extent possible, it is ''HIGHLY RECOMMENDED'' that the facility be actively managed to keep it dry before it freezes in the late fall. This can be done by various methods, including limiting inflow, under-drainage, and surface disking.</p>
 
<p>Even if the [[Glossary#I|infiltration]] properties of an [[Glossary#I|infiltration]] practice are marginal for snowmelt [[Glossary#R|runoff]], the storage available in the facility will provide some storage if it is dry entering the melt season. Routing the first highly-soluble portions of snowmelt to an [[Glossary#I|infiltration]] facility provides the opportunity for soil treatment (such as filtration, [[Glossary#A|adsorption]], microbial activity) of these solubles. Again, however, flow originating in an industrial area, a high traffic area where large amounts of salt are added, or another PSH should be diverted away from [[Glossary#I|infiltration]] systems.</p>
 
<p>Proprietary, sub-grade [[Glossary#I|infiltration]] systems provide an alternative to standard surface based systems. Essentially, these systems provide an insulated location for [[Glossary#P|pre-treated]] snowmelt to be stored and slowly infiltrated, or simply filtered and drained away if [[Glossary#G|ground-water]] sensitivity is an issue. The insulating value of these systems adds to their appeal as low land consumption alternatives to ponds and surface [[Glossary#I|infiltration]] [[Glossary#B|basins]].</p>
 
 
 
 
 
===Water Quantity Treatment===
 
<p>The amount of stormwater volume infiltrated depends on the design variant selected. Smaller [[Glossary#I|infiltration]] practices (e.g. [[Glossary#I|infiltration]] trenches) should either be designed off-line using a flow diversion, or designed to safely pass large storm flows while still protecting the i[[Glossary#I|infiltration]] area. In limited cases (e.g. extremely permeable soils), these smaller [[Glossary#I|infiltration]] practices can accommodate the channel protection volume, V<sub>cp</sub>, in either an off- or on-line configuration.</p>
 
<p>In general, supplemental stormwater practices will be necessary to satisfy channel and flood protection requirements when smaller [[Glossary#I|infiltration]] practices are used. However, these practices can help reduce detention requirements for a site through volume reduction. </p>
 
<p>Due to their size, the larger [[Glossary#I|infiltration]] practices (e.g. [[Glossary#I|infiltration]] [[Glossary#B|basins]] and underground [[Glossary#I|infiltration]] systems) have the potential to provide greater water quantity benefits. Surcharge storage above the practice bottom is available for detention. Outlet structures can be sized to partially or fully accommodate larger storm peak discharge control while allowing the volume below the outlet to infiltrate.</p>
 
 
 
 
 
===Water Quality Treatment===
 
<p>[[Glossary#I|Infiltration]] practices can remove a wide variety of stormwater pollutants through chemical and bacterial degradation, sorption, and filtering. Surface water load reductions are also realized by virtue of the reduction in [[Glossary#R|runoff volume]].</p>
 
<p>There are few data available demonstrating the load reductions or outflow concentrations of larger-scale [[Glossary#I|Infiltration]] practices such as [[Glossary#I|Infiltration]] trenches. Similarly, few sampling programs collect infiltrating water that flows through an [[Glossary#I|Infiltration]] system.</p>
 
<p>For properly designed, operated, and maintained [[Glossary#I|Infiltration]] systems, all water routed into them should be “removed” from stormwater flow, resulting in 100 percent efficiency relative to volume and pollutant reduction. For this reason, any [[Glossary#I|Infiltration]] [[Glossary#B|BMP]] performance table should show all 100 percent entries. This logic assumes that stormwater is the beneficiary of any [[Glossary#I|Infiltration]] system, but ignores the fact that pollution, if any remains after the internal workings of the infiltration [[Glossary#B|BMP]] itself (see later discussion in this section), is being transferred into the shallow [[Glossary#G|groundwater]] system. Good monitoring data on the [[Glossary#G|groundwater]] impact of infiltrating stormwater are rare, but there are efforts underway today to document this, so future Manual revisions should be able to include some data updates.</p>
 
 
 
 
 
<p>Properly designed [[Glossary#I|Infiltration]] systems discussed later in this section will accommodate a design volume based on the required [[Glossary#W|water quality volume]]. Excess water must be by-passed and diverted to another [[Glossary#B|BMP]] so that the design [[Glossary#I|Infiltration]] occurs within 48 hours if under state regulation, or generally within 72 hours under certain local and watershed regulations. In no case should the by-passed volume be included in the pollutant removal calculation.</p>
 
<p>Data that are reported in performance literature for [[Glossary#I|infiltration]] systems, unless reporting 100 percent effectiveness for surface water or documenting outflow water downward, are not accurately representing behavior, or are representing the excess flow (overflow) from a system. Design specifications in the following sections should prevent putting contaminated runoff and excess water beyond that which will infiltrate within the given timeframe. Any [[Glossary#R|runoff]] containing toxic material or excess volume that cannot infiltrate should be diverted away from the [[Glossary#I|infiltration]] system and reported as inflow to another treatment device.</p>
 
<p>Follow guidance and carefully use of [[Glossary#I|infiltration]] [[Glossary#B|BMP]]s to make sure they are not transporting highly loaded or toxic contaminants into the [[Glossary#G|groundwater]] system. These sections address the pollution remediation processes at work in [[Glossary#I|infiltration]] systems to reduce or totally remove pollutants that move through them. However, extreme caution must be exercised and serious planning undertaken to assure that no highly contaminating material is routed into these [[Glossary#B|BMP]]s. Of particular concern are toxic organics (gasoline, solvents) and high levels of chloride.</p>
 
<p>The [[Computer-aided design and drafting (CAD/CADD) drawings]]section contains details on how design and operations can either raise or lower the expected level of performance for [[Glossary#I|infiltration]] [[Glossary#B|BMP]]s.</p>
 
 
 
 
 
===Limitations===
 
<p>The following general limitations should be recognized when considering installation of [[Glossary#I|infiltration]] practices:</p>
 
*Limited monitoring data are available and field longevity is not well documented.
 
*Failure can occur due to improper siting, design, construction and maintenance.
 
*Systems are susceptible to clogging by [[Glossary#S|sediment]] and organic debris
 
*There is a risk of [[Glossary#G|groundwater]] contamination depending on subsurface conditions, land use and aquifer susceptibility.
 
*They are not ideal for stormwater [[Glossary#R|runoff]] from land uses or activities with the potential for high [[Glossary#S|sediment]] or pollutant loads.
 
*They are not recommended for areas with steep slopes
 
*Please not that even though there are potential pollution and physical clogging problems with [[Glossary#I|infiltration]], it is one of the most important elements in the stormwater [[Glossary#R|runoff]] treatment train. Fear of the limitations should not prevent well designed systems from being used.
 
<p>As noted in various sections, discussion of [[Glossary#B|BMP]] selection, the benefits associated with infiltration [[Glossary#B|BMP]]s should only be accrued based on the amount of water actually passing through the [[Glossary#B|BMP]]. Excess [[Glossary#R|runoff]] beyond that designed for the [[Glossary#B|BMP]] should not be routed through the system because of the potential for hydraulic and particulate over-loading, both of which will adversely impact the life and operation of the [[Glossary#B|BMP]]. .</p>
 
<p>For example, an infiltration device designed to treat the first 0.5 inch of runoff from a fully impervious surface will catch about 30 percent of the volume of runoff in the Twin Cities. This means that 70 percent of the runoff volume should be routed around the filtration system and will not be subject o the removals reflected in the above tables. Attributing removal to all [[Glossary#R|runoff]] just because a [[Glossary#B|BMP]]. is in place in a drainage system is not a legitimate claim.</p>
 
 
 
 
 
{{alert|It is ''REQUIRED'' that some form of [[Glossary#P|pre-treatment]], such as a plunge pool, sump pit, filter strip, sedimentation [[Glossary#B|basin]], grass channel, or a combination of these practices be installed upstream of the [[Glossary#I|infiltration]] practice.|alert-danger}}
 

Latest revision as of 22:40, 23 November 2022

Information: This section on infiltration trench includes information for infiltration trench and infiltration basin. We anticipate reorganizing this section and eventually having individual sections for infiltration trench, infiltration basin, and bioretention-bioinfiltration

Infiltration basin

An infiltration basin is a natural or constructed impoundment that captures, temporarily stores and infiltrates the design volume of water over several days. 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 12 feet, including bounce in the basin. An infiltrates basin construction detail is located in the drawings section.

Infiltration trench (a.k.a. infiltration gallery)

An infiltration trench is a shallow excavated trench, typically 3 to 12 feet deep, 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. Trenches are commonly used for drainage areas less than 5 acres in size.

Warning: 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.

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. 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.


Related pages

This page was last edited on 23 November 2022, at 22:40.