- Topsoil may be material that was stripped from the project site and stored in stockpiles for re-use, or material imported to the site from a supplier provided the physical and chemical characteristics are within acceptable ranges.
- Topsoil shall be in compliance with Ontario Regulation 153/04 Record of Site Condition standards for soil quality or as amended through Ontario Management of Excess Soil - A Guide for Best Management Practices.
- Soil laboratory reports shall certify the material to be suitable for re-use on residential, parkland, institutional, industrial, commercial, or community landscapes for the germination of seeds and the support of vegetative growth.
The factors to consider in determining if a topsoil is suitable for use as planting soil for a vegetated stormwater practice include the following:
- Must be friable and capable of sustaining vigorous plant growth;
- Must be free from toxic material and roots, stones or debris over 50 mm (2") in diameter;
- Should not have been passed through sieves or screens smaller than 50 mm (2”) to avoid eliminating peds;
- Should have a Loamy Sand, Sandy Loam, Sandy Clay Loam, Loam or Silty Loam soil texture;
- Must contain a minimum of 5% organic matter by dry weight;
- Must have a pH of between 6.0 and 7.8;
- Must have a sodium absorption ratio less than 15;
- Must have a cation exchange capacity of greater than 10 milliequivalents per 100 grams (meq/100 g).
Specify that 4 litre samples of topsoil, from each source to be drawn upon, be provided to the consultant for visual inspection, along with topsoil quality test results from an accredited soil testing laboratory, or a quality assurance certificate from the supplier.
We recommend a planting soil depth of 300 mm for grasses, 600 mm for shrubs and perennials, and 1000 mm for trees.
For use in producing a bioretention filter media blend, specify that the topsoil used must contain at least 9%, and not greater than 36% clay-sized particles.