Trench, chamber, and perforated pipe: Installation

The guidance provided in this section is applicable for the construction of soakaway pits, infiltration chambers, infiltration trenches, and exfiltration pipes of varying size and shape, since the installation of each of these features is similar.

An excavator covering units of unfinished infiltration chamber rows with perimeter stone. Stone can be applied progressively as the rows are completed to ensure that space is provided for the excavator to work within the LID footprint. Photo Source: Municipal Sewer & Water

1. Apply clear stone to the floor of the excavation to act as the base for chambers, pipes, and trenches.
2. For infiltration chamber construction, install chamber feeder-pipes to the top of the base, connecting to the inlet control manhole, where applicable.
3. Roll out scour fabric length-wise beside any feeder-pipes that have been installed, if specified in the design.
4. If specified, lay out scour fabric where the base of the infiltration chamber, soakaway, or pipe is anticipated to be installed. No seams should be present where the fabric underlies chambers.
5. Install chambers, trenches, or perforated pipes at the location and elevation specified in the contract documents. Where infiltration chambers need to be assembled from units, install each piece of the chamber row, as per the manufacturer’s instructions, until the entire length of the chamber is in place. The ends of the chamber may be installed just prior to perimeter stone being applied to the ends of the rows, if desired, to ensure ease of inspection.
6. Connect any perforated pipe connections, underdrains, roof leaders, or observation wells at the appropriate elevations, per the design.
7. With a stone conveyor or excavator, begin placing clear stone as specified in the design. For domed chambers, place stone along the centreline of the chamber rows. Doing so will distribute stone to either side of the chamber, anchoring each side in roughly equal proportion.
8. Backfill the excavated area with clear stone to the depth specified in the contract documents. Ensure that the depth of stone does not differ by more than 300 mm between the sides of any given chamber row at any point during the backfilling process.
9. Once backfilling is complete, level the perimeter stone with a small dozer. Only push material in the direction parallel to the rows.
10. If specified by the design, roll geotextile parallel to rows over the top of stone. Provide sufficient overlap, as specified by the manufacturer.

Note: where many rows of infiltration chambers are being installed, it may be advisable to construct the chamber rows piece-wise as the application of perimeter stone progresses to provide space for excavators to apply the stone from on top of the stone base. See the adjacent photo for an example.

Key Inspection Points:

• Feeder-pipes protrude into the storm chambers at the appropriate length, per manufacturer’s specifications.
• Scour fabric does not overlap beneath the walls of open-bottom chambers.
• Minimum distance between adjacent chambers is provided.
• Minimum depth of stone below and stone above chamber is provided, per manufacturer specifications.
• Depth of chamber inverts are installed correctly, relative to the elevation of the inlet, such that the storage potential of chambers are maximized.
• Infiltration chambers are assembled as specified by the manufacturer.
• Perimeter stone extends to the excavation walls.
• LID practice is protected with applicable ESC to avoid contamination of infiltration area or materials.

Mistakes to Avoid:

• Equipment on the perimeter stone – Perimeter stone should be applied with a stone conveyor or excavator from the outside of the LID footprint or on the stone foundation.
• Uneven perimeter stone – Perimeter stone must be applied such that the depth of stone on one side of the chamber is not unacceptably higher than the other. Refer to design details.
• Incorrect inlet elevation – For applications where infiltration chambers overflow into a sewer, it is important that the top of chamber is positioned at an elevation below the lowest invert of the other sewer connections. Otherwise, only part of the chamber volume can be utilized.
• Damaged or missing ESC – Ensure that ESC protection is adequately inspected
• Putting system online prematurely - Do not allow the feature to receive stormwater when contributing drainage area is not stabilized and sediment and debris is present.

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  Chamber resting on top of scour fabric at Alton Main Street.

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  Components of an infiltration chamber being overlapped.

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  Example of "crate style" Infiltration chambers being installed in East Gwillimbury. Photo credit: Make-Way Environmental Technologies Inc.

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  Example of an infiltration chamber system under a parking lot.]

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  Infiltration trench equipped with a perforated pipe.]

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  Manifold connecting to infiltration chamber rows. Photo provided by Advanced Drainage Systems.

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  Scour fabric rolled out below an infiltration chamber during assembly. Photo provided by Advanced Drainage Systems.

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  A storm chamber inlet protected from debride by an envirohood. It is essential that the top of the chamber is lower in elevation than any other outlets from the catchbasin. This is because the chamber’s capacity should be fully utilized before runoff is allowed to travel farther downstream.

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An underground water storage reservoir into which stormwater is directed and allowed to percolate into the underlying native subsoil.

An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits.

The downward movement of water through the soil, the downward flow of runoff from the bottom of an infiltration BMP into the soil.

Loss of water from a drainage system as a result of percolation or absorption into the surrounding medium (e.g., the infiltration of water into the native soil through a perforated pipe wall as it is conveyed).

Low Impact Development. A 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.

Filter 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.

The 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.

Soil, 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.

Box like underground concrete structure with openings in curb and gutter designed to collect runoff from streets and pavement.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.