Construction: pretreatment and inlet

Pre-treatment structures are most cost effective when they slow down incoming flows, collect sediment for easy clean out, and slowly release water to the bioretention facility mitigating erosion. Pretreatment structures/strategies can include curb cuts, Aggregates, proprietary devices like filters or hydrodynamic separators, vegetation, concrete sumps, membrane filters, overland flow sumps, etc.

Construction Steps:

• Installation of pre-treatment features will vary based upon type. Similarly, installation timeline will range with type and could occur at excavation and mass grading, curb work or at finishing grade. Given pre-treatment features are typically integrated with the LID inlet coordination amongst multiple sub-contractors is sometime needed. The following details steps for various pre-treatment types:
• Vegetation: Follow the guidance shown below in the section “Plant Material Verification and Installation”
• Curbing: Follow the guidance shown above in the section “Curbing”.
• Aggregate: Follow the guidance shown above in the section “Stone reservoir”.

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  Aggregate material (rock) installed as the inlet and pre-treatment device in the rain garden at Glendale P.S. in Brampton, ON. The runoff comes from a vegetated swale into the inlet, conveying it into the rain garden. (Photo Source: CVC, 2021)

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  Aggregate material (rock) installed as the inlet and pre-treatment device in the rain garden at Glendale P.S. in Brampton, ON. The runoff comes from a vegetated swale into the inlet, conveying it into the rain garden. (Photo Source: CVC, 2021)

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  Aggregate material (rock) installed as the inlet and pre-treatment device in the rain garden at Glendale P.S. in Brampton, ON. The runoff comes from a vegetated swale into the inlet, conveying it into the rain garden. (Photo Source: CVC, 2021)

Proprietary pre-treatment device

1. Excavate and prepare base for proprietary pre-treatment device according to design.
2. Install proprietary pre-treatment device according manufacturer directions.
3. Manufacturer representative may need to confirm proper installation and functioning through approved testing and inspection.
   

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  Installation of Jellyfish filter and sorbtive media vault at the IMAX bioswale project in Mississauga, ON. (Photo Source: CVC, 2012)

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  Installation of Jellyfish filter and sorbtive media vault at the IMAX bioswale project in Mississauga, ON. (Photo Source: CVC, 2012)

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  Installation of Jellyfish filter and sorbtive media vault at the IMAX bioswale project in Mississauga, ON. (Photo Source: CVC, 2012)

Key Inspection Points:

• Verify that the correct pre-treatment device (jellyfish filter, vegetation, curbing, etc.) is being installed.
• Verify that all components of the pre-treatment device are installed
• Verify correct size and location of pre-treatment device.
• Verify correct elevation, slope, and footing according to design
• Is it tied into the curb, downspout, or other inlet? Or could happen before the curbing?
• Wet weather performance check:
  • Does it work?
  • Is water entering the LID facility properly?
  • Is sediment and debris accumulating?
  • Is it dissipating erosive forces?

Mistakes to Avoid:

• Pre-treatment component parts are missing
• Grading/elevation errors that deviates from design
  • Incorrect pipe inverts causing short circuiting
  • Insufficient grade drop or slope into pre-treatment to ensure positive flow of water
  • Improper grading from pre-treatment to LID feature inhibiting positive flow
  • Insufficient sump depth to account for sediment and debris accumulation
• Using wrong concrete forms if concrete curbs are part of pre-treatment.

For more information about pre-treatment strategies and their design, visit these page: Pretreatment and Pretreatment features.

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.

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

(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).

Open space floodway channels, road reserves, pavement expanses and other flow paths that convey flows typically in excess of the capacity of the Minor Drainage System.

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.

A 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.

An underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe.

A lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts.

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.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Credit Valley Conservation

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.