California Department of Transportation
 

Local Topsoil

Topsoil

What is This Treatment?

Local topsoil is topsoil obtained from within the project limits and includes removing, stockpiling, and placing local topsoil on areas disturbed by construction activities.

Local topsoil is the one of the most effective methods to establish vigorous vegetative coverage because local topsoil typically contains the ideal physical, chemical and biological properties to establish vegetation.

Where to Use This Treatment:

  • Typically applied on slopes 1.5:1 (H:V) and flatter. The following application rates are suggested:
    • Slopes 1.5:1 (H:V) - 2" maximum thickness.
    • Slopes 2:1 (H:V) - 3" maximum thickness.
    • Slopes 3:1 (H:V) - 4" maximum thickness.
    • Slopes ≤ 4:1 (H:V) - 6" maximum thickness.
  • Caltrans Highway Design Manual Topics 110.2(2) and 110.2(4) recommend considering the use of Local Topsoil to treat disturbed soil areas to help protect stormwater runoff quality.

Benefits:

  • Reduced stormwater runoff volume and velocity.
  • Improved infiltration rate.

  • Improved soil water holding capacity.

  • Improved soil structural properties - soil structure, porosity, and texture.

  • Improved soil chemical properties - providing proper pH, carbon, nitrogen, potassium and phosphorus levels.

  • Improved soil biology - activity by bacteria, mycorrhizal fungi, nematodes, protozoa, microarthropod and earthworms.

  • Improved soil nutrient levels and nutrient cycling.

  • Improved potential for vigorous long term vegetation coverage.

Limitations:

  • More costly (yet more effective) than surficial treatments such as Erosion Control (Hydroseed).

  • Requires temporary storage space within the project limits to stockpile materials.

  • Requires removal of noxious weed species prior to harvesting of materials from the project site.

  • Requires site accessibility by earthwork equipment.

Specifications:

In the 2010 specifications, specify Local Topsoil as follows. (1) Local Topsoil is defined in the 2010 Specifications in Section 21-1.02D Topsoil. This definition of Local Topsoil references Section 19-2.03D Selected Material, which provides additional information on how to handle Local Topsoil. (2) Because Local Topsoil is specified as Selected Material, Local Topsoil is paid for as Roadway Excavation. (3) Show the areas to be excavated and areas to be applied on the plans. (4) Include the bid item for Roadway Excavation in the Bid Item List.

Consider Using This Specification With:

To provide protection for the soil surface, consider combining this treatment with:

  • Hydroseed
  • Duff - a duff layer reduces raindrop impact erosion and serves as a source of native seed and mycorrhizal fungi.
  • Compost with seed applied at the same time.

Plans and Details:

  • There is no Standard Plan for Topsoil

Estimate Information:

  • No BEES Code, Local Topsoil is paid for as Selected Material.

Guidance:

External Links:

Updated 04-15-2014