Infiltration chambers

From LID SWM Planning and Design Guide
Revision as of 14:11, 27 July 2018 by Jenny Hill (talk | contribs) (Plastic chambers)
Jump to: navigation, search

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 OPSS 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 following presents a summary of considerations when planning the construction of a low impact developmentA stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. project. More details can be found in the following reference:[3]

  • 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.

Sequencing

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.


  1. Excavate subsurface water storage reservoir to base elevation,
  2. Check base elevation and slope,
  3. Fracture/rip bottom and roughen side of the excavation to remove smeared surfaces,
  4. Install optional geotextiles (or liner for biofilter); overlapping according to design drawings,
  5. Install coarse reservoir gravel, and any void forming structures (e.g. underdrains, infiltration chambers, or wells),
  6. Check elevation and slope at top of reservoir,
  7. Install choking layer and optional geotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils. (typically only over the perforated pipe),
  8. Check elevation and slope at top of choking layer,
  9. Install filter media with additional 30 cm over finish grade of the filter bed,
  10. Thoroughly saturate and allow to settle for at least one week. After this time, tamp manually to check settling is complete. Alternatively, installations made in the fall can be left to settle over the whole winter season at this point,
  11. Install temporary erosion and 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. control practices,
    Conduct all other site construction activities (buildings/servicing etc.)
  12. Check condition of bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. after settling period, remediate any deficiencies,
  13. Install curbs and pavements and concrete pretreatment devices,
  14. Check elevations of curb cuts and other inlets
  15. Install erosion controlIncludes the protection of soil from dislocation by water, wind or other agents. to all inlets!!
  16. Remove excess filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. along with any accumulated construction 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.,
  17. Install any surface applied additives,
  18. Conduct fine grading to surface of filter bed, checking elevations/slopes/compaction,
  19. Apply stone or mulch cover for decorative systems, or turf reinforcement for grassed systems,
  20. Install erosion control blankets or matting
  21. Plant or lay sod,
  22. Saturated system thoroughly to settle filer media particles around the roots of new plants,
  23. Irrigated the system as required to establish healthy vegetation cover,
  24. Inspect and remediate deficiencies after any significant rainfall within the next 3 months or remainder of the first growing season.



Facilities containing media

BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Sequencing depends on the design:

  • Full infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.:Pack 50 mm diameter clear stone to storage design depth, top with 100 mm of the choker course,
  • Partial infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.:Place design depth of 50 mm diameter clear stone for the infiltration volume on bed and then lay the perforated underdrainA perforated pipe used to assist the draining of soils. pipe over it. Pack more clear stone to 75 mm above the top of the underdrainA perforated pipe used to assist the draining of soils., top with 100 mm of choker layer.

Stormwater planters

  • Place an impermeable liner on the bed with 150 mm overlap on sides. Lay the perforated underdrainA perforated pipe used to assist the draining of soils. pipe, Pack 50 mm diameter clear stone to 75 mm above top of underdrainA perforated pipe used to assist the draining of soils., top with 100 mm of choker layer;

Rain gardens

No storage or drainage is required, filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. or amended topsoil is laid onto native soils

Media installation

Media installed over the choker course in 0.3 m lifts until desired top elevation is achieved. Each lift must be thoroughly wetted and drained before adding the next. Wait three weeks to check for settling, and add additional media and regrade as needed.

  • Prepare planting holes for any trees and shrubs, install vegetation, and water accordingly.
  • Install any temporary irrigationHuman application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47.
  • Plant landscaping materials as shown in the landscaping plan, and water them weekly in the first two months.
  • Lay down surface cover in accordance with the design (mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales., riverstone, or turf).
  • Conduct final construction inspection, checking inlet, 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., bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cell and outlet elevations.
  • Remove erosion and 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. controls, only when the entire 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 stabilized.

Checklists



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
  3. [https://cvc.ca/wp-content/uploads/2013/03/CVC-LID-Construction-Guide-Book.pdf Construction Guide for Low Impact Development, CVC (2013)