Infiltration chambers

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Overview

As their name suggests infiltration chambers work exclusively to infiltrate stormwaterSurface runoff from at-grade surfaces, resulting from rain or snowmelt events.. They are an underground facility and are often used beneath parking lots or playing fields to treat flow routed from other areas.

Infiltration chambers are an ideal technology for:

  • Installing below any type of surface or landscape
  • Receiving and infiltrating large volumes of water

The fundamental components of an infiltration gallery are:

  • Structurally reinforced chambers
  • Layers of coarse aggregate to bed the chambers and redistribute water.
  • Pipe
System type Pipe Vaults Arched chambers Crates
SWM Pipe.jpg SWM Vaults.jpg SWM Arches.jpg SWM Crates.jpg
Materials Plastic Concrete Plastic/concrete Plastic
Footprint Medium Small Large Small
Stackable Not usually (can be without infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.) Yes Not usually (can be without infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.) Yes
Onsite assembly Some No Yes Yes
Void ratio 60-65% 75-85% 50-65% 95%
Maintenance access Moderate Excellent Moderate Difficult
Standard strength H-20 H-25 H-20 H20-HS25
Manufacturer Contech "Contech Stormtrap Rotondo" "Contech Stormchamber Cultech" "Ecorain Atlantis Stormtank"

Planning Considerations

Both modular systems require a lower bedding layer of angular stone to permit infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., and provide a foundation for the installation:

  • Plastic modules usually have a parabolic shape to resist the load above. The spaces between the rows of the gallery are then filled with more clear stone to support the overlying infrastructure.
  • Concrete modules are often box shaped and can, in some circumstances, be employed without any additional cover. However, a minimum of 20 cm cover is for most applications. Where this cover is (irrigated) topsoil this can support turf grass. Deeper soil is required to support more complex plants.

Design

Sizing

Infiltration: Sizing and modeling

Modeling

Materials

Chambers

Plastic chambers

Chambers should be compliant with:

Allowable loads for the chambers must be determined in accordance with ASTM F2787-13 “Standard Practice for Structural Design of Thermoplastic Corrugated Wall Stormwater Collection Chambers”.

Concrete chambers

Chambers should be compliant with:

AggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Note the uniform size and angularity of this clear stone sample. Note also that the fragments all appear to have a film of fine particles adhering; this material would be improved by being washed prior to use.

This article gives recommendations for aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. to be used to store water for infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.. This is usually called 'Clear stone' at aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. yards. To see an analysis of Ontario Standard Specifications for granularGravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices. materials, see OPS Aggregates. For advice on decorative surface aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. see Stone

Gravel used for underdrains in bioretention, infiltration trenches and chambers, and exfiltration trenches should be 20 OR 50 mm, uniformly-graded, clean (maximum wash loss of 0.5%), crushed angular stone that has a void ratio of 0.4[1].

The clean wash to prevent rapid accumulation of finesSoil particles with a diameter less than 0.050 mm. from the aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. particles in the base of the reservoir. The uniform grading and the angularity are important to maintain pore throats and clear voids between particles. (i.e. achieve the void ratio). Porosity and permeability are directly influenced by the size, gradation and angularity of the particles [2]. See jar test for on-site verification testing protocols.

Gravel with structural requirements should also meet the following criteria:

  • Minimum durability index of 35
  • Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions

Standard specifications for the gradation of aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. are maintained by ASTM D2940


Other

Construction

  • The site of the infiltration facility must remain outside the limit of disturbance and blocked from site traffic until construction of the facility begins, to prevent soil compaction by heavy equipment.
  • This area must not be used as the site of sedimentSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. basinsGround depression acting as a flow control and water treatment structure, that is normally dry. during construction, as the concentration of finesSoil particles with a diameter less than 0.050 mm. will reduce post-construction infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface..
  • This area must not be use as a staging area, for storing materials.
  • To prevent sedimentSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. from clogging the surface, stormwater must be diverted away from the facility until the drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. is fully stabilized.
  • As many infiltration facilities are installed in the road right-of-way or tight urban spaces, considerations of traffic control and utility conflicts must be part of the plans and inspections.

The following is a typical construction sequence to properly install an infiltration practice:

  1. The area should be fully protected by siltSoil or media particles smaller than sand and larger than clay (3 to 60 m) fence or construction fencing to prevent compaction by construction traffic and equipment,
  2. Installation may only begin after entire contributing drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. has been either stabilized or flows have been safely routed around the area. The designer should check the boundaries of the contributing drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. to ensure it conforms to original design,
  3. The pretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms. part of the design should be excavated first and sealed until full construction is completed,
  4. Excavators or backhoes working adjacent to the proposed infiltration area should excavate to the appropriate design depth,
  5. The soil in the bottom of the excavation should be ripped to promote greater infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.,
  6. Any accidental sedimentSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. accumulation from construction should be removed at this time,

Gallery

External links

In our effort to make this guide as functional as possible, we have decided to include proprietary systems and links to manufacturers websites.
Inclusion of such links does not constitute endorsement by the Sustainable Technologies Evaluation Program.
Lists are ordered alphabetically; link updates are welcomed using the form below.

Plastic chambers

Concrete chambers


  1. Porosity of Structural Backfill, Tech Sheet #1, Stormtech, Nov 2012, http://www.stormtech.com/download_files/pdf/techsheet1.pdf accessed 16 October 2017
  2. 2.0 2.1 2.2 Judge, Aaron, "Measurement of the Hydraulic Conductivity of Gravels Using a Laboratory Permeameter and Silty Sands Using Field Testing with Observation Wells" (2013). Dissertations. 746. http://scholarworks.umass.edu/open_access_dissertations/746