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Guideline S.3 Soil Management

Intent

To promote the maintenance of the permeable structure of the soil in order to optimize water infiltration/filtration capabilities and maintain the biological functions of the soil in order to optimize plant health and species richness.

Required Performance Criteria

Guidelines apply to all projects designated New Buildings and Major Renovations with site work site scope that includes an area of site disturbance that is greater than 3,000 s.f. OR Area of imperviousness (footprint of building plus site impervious area) renovated that is greater than 2,000 s.f.

  1. Create soil management and erosion control plans to protect the soil profile of the site during and after construction.
  2. The bulk density of all unpaved pervious surfaces intended for seeding and planting must have the following maximum bulk densities. Soils in these areas that exceed the stated bulk densities must be decompacted to 18 inches prior to planting or seeding by air spading, ripping, adding organic matter (see S.3F), or other decompaction method.
    1. Clay and Silt: less than 1.25 g/cm3.
    2. Loam: Less than 1.35 g/cm3.
    3. Sand: Less than 1.55 g/cm3.
  3. Limit soil disturbance.
    1. Limit soil disturbance (defined as grading, compacting, piling, tilling, scraping, storing, and removal of soil) to 40 feet beyond the building perimeter; 15 feet beyond primary roadway curbs, main utility branch trenches, pervious areas, and stormwater management features; and 5 feet beyond walkways.
    2. Limit soil disturbance to no closer than 5 feet from tree driplines and/or the perimeter of site areas/features identified for protection. Trees must be protected as individuals or as groups (canopies < 10 feet apart) with tree protection fence located 5 feet beyond the drip line, prior to site activities.
  4. Maintain, establish, or enhance a 75-foot vegetated buffer for delineated wetland boundaries.
  5. Do not sell or export any topsoil from project site. Stockpile and protect existing site topsoil, or import topsoil for a respread of 12 inches in all proposed planting and seeding areas.
  6. Build the site’s natural mycorrhizae and microbial population and enhance the health of the soil by raising or maintaining the percentage of organic material content in the existing or imported site soil. Soil must have a minimum of 3% organic material by weight. Test the soil in planting and seeding areas and amend with organic material as needed to meet this requirement.
  7. Where trees are surrounded by hard surfaces (e.g., sidewalks, patios, driveways, car parks, plazas, parking islands), use suspended pavement techniques, structural soils, or other comparable methods such as larger tree openings to provide adequate rootable soil volumes. Minimum volume of rootable soil volume per tree is:
    1. Small trees (e.g., serviceberry): 400 cubic feet
    2. Medium trees (e.g., ironwood): 800 cubic feet
    3. Large trees (e.g., hackberry): 1,200 cubic feet

Note: If using structural soils, total soil volumes above need to be multiplied by 5 to obtain equivalent volume of soil useable by the tree. If above soil volumes cannot be met, trees requiring smaller soil volumes should be selected. Where applicable, utilize suspended pavement or comparable methods to allow tree roots under hard surfaces access to adjacent open space.

Implementation in the Design Process:

When the site is selected, a soil management plan must be drafted and updated to prevent erosion, maintain and protect topsoil, amend soil, and provide adequate soil rooting volume to grow large, healthy trees per the B3 Guideline requirements.

Submittals for compliance should be monitored to ensure that the B3 Guidelines will be met in the construction documents, construction administration, and project buyout to ensure that performance criteria are being met.

A preconstruction meeting should be held to identify requirements for protection, preservation, and enhancement of site soil during and after the construction process. Practices to meet performance criteria should be implemented according to the drawings and specifications and successful implementation of performance criteria should be confirmed when complete.

Documentation:

The documentation required for this guideline includes the following:

  • Soil management and erosion control plans.
  • Verification of language mandating compliance in construction documents and verification of meeting guideline requirements for maximum bulk densities, applicable wetland requirements, prohibition of topsoil removal from site, minimum organic content, and protection of trunk area.

Final Design:

  • S.3A: Soil management and erosion control plans.
  • S.3B: Verification that the construction documents mandate compliance.
  • S.3C: Verification of the site plan meeting guideline in construction documents.
  • S.3D: Verification that if wetlands are on the site that the appropriate buffer has been established or maintained.
  • S.3E: Verification of language mandating compliance in construction documents.
  • S.3F: Verification of language mandating compliance in construction documents.
  • S.3G: Verification of language mandating compliance in construction documents if trees are surrounded by hard surfaces.

Closeout:

  • S.3B: Verification of meeting the guideline requirements.
  • S.3C: Verification of the final site plan meeting guideline. Verification that the site contractor understands the requirements and intent of this guideline.
  • S.3D: Verification that if wetlands are on the site that the appropriate buffer has been established or maintained.
  • S.3E: Verification of language mandating compliance in construction documents as updated during construction and verification that the site contractor understands the requirements and intent of this guideline.
  • S.3F: Verification of language mandating compliance in construction documents as updated during construction and verification that the site contractor understands the requirements and intent of this guideline.
  • S.3G: Verification of language mandating compliance in construction documents and guidelines requirement compliance if trees are surrounded by hard surfaces.

Philip J. Craul. Urban Soils: Applications and Practices. New York: John Wiley & Sons, 1999.

Bassuk, Nina; Grabosky, Jason; Trowbridge, Peter; Urban, James. “Structural Soil: An Innovative Medium Under Pavement that Improves Street Tree Vigor.” Urban Horticulture Institute, University of Michigan. Web resource from: www.hort.cornell.edu/uhi/outreach/csc/article.html

University of Minnesota Extension: www.extension.umn.edu

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