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Line 5: − + + + + + + + + + + − + + + − Avoid creating a "bathtub" effect where isolated areas of coarser soils or loamy sands are surrounded by fine soils or clay. The design engineer and landscape architect should review both subsoil and topsoil materials for compatibility of compactness and texture in planting areas of the LID Practice. Methods, such as soil amendment and preparing a larger planting bed, may be required to prevent discontinuous soil layers. In bioretention practices with a loamy sand soil media placed in clay soil textures, an underdrain is necessary.
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The factors to consider in determining a suitable soil mix for a vegetated stormwater practice include the following:
The factors to consider in determining if a topsoil is suitable for use as planting soil for a vegetated stormwater practice, or use in producing a bioretention filter media mixture 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;
* For use as planting soil for a vegetated stormwater practice , the topsoil must contain a minimum of 5% organic matter by dry weight or be amended so, through addition of an organic soil conditioner;
* For use in producing bioretention filter media Blend B (water quality treatment priority), the topsoil must contain at least 9%, and not greater than 36% clay-sized particles and at least 2% organic matter by dry weight.
* Must have a pH of between 6.0 and 8.0;
* Must have a sodium absorption ratio less than 15;
* Must have a cationic exchange capacity greater than 10 milliequivalents per 100 grams (meq/100 g).
Specify that topsoil must be friable, neither heavy clay nor of a very light sandy nature. An example of sandy loam topsoil is 60 % sand, 25 % silt, 10 % clay, organic matter 5 % and pH value of 6 - 7.5. Topsoil must be capable of sustaining vigorous plant growth and to be free from subsoil, roots, vegetation, debris, toxic materials and stone over 50 mm diameter. Specify that topsoil sample must be provided to the consultant for testing and analysis including herbicide or atrazine content. All topsoil supplied must conform to a sample provided. Minimum topsoil depth is 150 mm for turf areas and ranging to 1.25 m for perennials, shrubs and trees.
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 or filter media depth of 300 mm to support grasses, 600 mm for shrubs and perennials, and 1000 mm for trees.
[[category: materials]]
[[category: materials]]