Construction: soil media and amendment

Bioretention can be constructed over any soil type, but hydrologic soil group A and B are best for achieving water balance objectives. Facilities designed to infiltrate water should be located on portions of the site with the highest infiltration rates. STEP has detailed construction guidance on soil amendments available on its [Construction Specifications for Implementing Compost Amended Planting Soil in Ontario] webpage. These resources include specification details and a spreadsheet calculator for determining soil and amendment volumes.

Construction Steps:

1. Apply soil media in 150-300 mm lifts until desired top elevation of bioretention, bioswale or rain garden area is achieved.
2. Apply soil media with slinger trucks when possible. This type of equipment will reduce the need to move soil media manually or by backhoe.
3. Thoroughly wet each lift before adding the next and wait until water has drained through the soil before adding the next lift.
4. If amending soils:
   
   • Stockpile native soils in designated areas.
   • Mix selected additives with native soils using appropriate equipment.
   • Sling soils into the LID feature whenever possible.

Key Inspection Points:

• When material arrives to the site: perform chain of custody, visual inspection and ribbon test to ensure that material meets design requirements.
• Soil/filter media’s design parameters and assumptions should be confirmed through in-situ permeability testing (e.g., permeameter measurements to determine hydraulic conductivity). Results of permeability testing should be reviewed by the designer and, if required, changes to the LID design may be needed. See Testing for more information regarding testing procedures.
• Ensure that soil media is being applied to the correct depth.
• Ensure that the native soil and amended material are well blended.
• Measure potentially compacted soils using a cone penetration test or a cone penetrometer.

Mistakes to Avoid:

• Machine compaction: Equipment should not be operated within the infiltration practice.
• Soil material: Accepting material that does not meet design specifications and requirements.
• Application: Applying the next lift without letting dry the previous lift of filter material.

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

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

Sustainable Technologies Evaluation Program

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

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.

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

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.

The 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.

A parameter that describes the capability of a medium to transmit water.

The natural ground material characteristic of or existing by virtue of geographic origin.