Soil Resource Plan (aka Drawing A Line In The Caliche}

One of the new requirements in the 2018 Article X amendments placed on new developments is the provision for a soil resource plan.  This plan is essentially a map showing zones of general soil types, quality, compaction, and other factors considered for planting and preserving trees.  It is designed to reveal zones reserved for development from those for landscaping.  And for the landscape areas, the plan will reveal how each zone is either protected from construction or restored from the heavy compaction of most development impact areas.  Our goal is for the contractor to have a recognition and a plan to identify the areas on a building site where a healthy tree will grow on the development site with or without soil preparation.

Let's go over the process for this document.  We will address the soil resource assessment later.

(b) Soil areas.  Except as provided in this section, required landscape areas must include the following:

   (1) Soil resource plan.  A soil resource plan is required with the submission of a landscape plan or tree protection plan. A soil resource plan is used to distinguish landscaping zones from construction zones on the building site and to determine soil protection or soil modification for vegetation, if applicable. Zones that are required to be shown include:

(A) protected zones where existing soil and vegetation will not be disturbed;

(B) zones for soil amendment or treatment with minimal disturbance;

(C) zones where construction traffic and staging will be allowed; and

(D) zones for stockpiling topsoil and imported soil amendments.

The soil resource plan can be included in the landscape/tree protection plan with the permit set or can be separated into a separate document.  The best course of action preceding construction plan review would be to submit the documents to the city arborist as early as possible, along with engineering studies, to assure a suitable review process has been engaged.  The report from the arborist could be made ready before permits are issued or while in a review.

Essentially, the resource plan is a map and a prescription of work to help the general contractor to direct the flow of construction activity with an awareness of the potential for soil damage. If an area is heavily compacted and to be used for future landscaping, this particular area may need a soil preparation process with amendments to make the soil bed ready for receiving trees and other vegetation.  It also does not serve to damage the owner's property. The Landscape and Tree Manual Section 5 - Urban Soils provides information on retaining a healthy soil, how to test for the conditions, and methods on how to amend the soils for planting after severe compaction has occurred by using techniques like topsoil fracturing.  The process loosens and recharges the soil to make ready a healthier growing site for newly planted nursery stock trees.  It's not a process for around large established trees on the site.

The plan will at first separate the designated landscape areas from the impervious and developed portions of the building site, including areas of infrastructure installation.  The level of detail on the plan will depend on how the designer intends to communicate with both city staff, the general contractor, irrigator, and the landscape contractor on how certain areas may be avoided from construction practices while concentrating staging and construction activity elsewhere.  This may help minimize the amount of preparation work and cost to make a site ready to receive trees in a healthy soil condition.

The designated landscape areas should then be listed as undisturbed, minimally disturbed, heavy construction, or soil stockpiling.  The best method may be to indicate a zone by shading and a letter reference ("A", "B", etc.) and to indicate the specifics of the letter zone in a small table. Additional zones may be identified to specify a need to protect an area or to encourage construction traffic to a separate zone.

Undisturbed areas should include areas in proximity to existing large trees on the property going out as far from the center of the tree as possible.  On any construction site, any tree retained in proximity to a development impact area of construction will be damaged.  The goal here, and in all construction projects, is to minimize that damage.  If the tree is strong enough and in suitable soil conditions, the tree can long endure the stresses of construction.

If an area is minimally disturbed, and a candidate for soil amendments and treatments, the process of soil treatment will depend on the severity of the impact.  Even slightly damaged soils may still need a fracturing process if the site is even moderately compacted, but areas near large trees may need more selective and less intensive soil intrusion to minimize tree root damage.

The areas of heavy construction will be areas to be considered for landscaping last and which will require the most significant preparation work to make ready for new tree planting or other site improvements.  These areas may also include sites of intensive excavation and grading and the removal of topsoils in the construction area.  The area will probably be a good candidate for soil fracturing prior to tree installation and should be remediated if hazardous chemical activity may have occurred in the area.  Prep the soil with organics as needed in the soil treatments prior to tilling.

Moved topsoils should be stockpiled on site and made ready to be used for landscape areas.  A practice which needs to be avoided is the planting of trees in mineral soils which are severely deficient in organic nutrients and essential elements for the tree.  Topsoil storage is a practice not utilized enough and needs to be increased for maintaining new landscaping on the site.

A critical feature to maintaining these soil resource areas is in protecting them with the required tree protection fencing and other materials as specified in Section 51A-10.136.  The ordinance has been amended to increase the standards for more rigid and structured chain link fencing to be applied in certain circumstances around trees. Fence where it is needed around existing trees to the drip line or critical root zone, whichever is farthest from the tree stem, and apply other best management practices for soil management on the construction site.

There are multiple resources to assist with this practice.  I encourage you to look to how you can best use this tool to help guide the construction practices to help protect the existing trees on the work site while also creating the best conditions for the future trees to be planted.

The following links are extremely helpful in understanding the soil dynamics on a work site.

Protecting Urban Soil Quality

Soil Profile Rebuilding - Virginia Tech
A Guide To Preventing Soil Compaction During Construction - Alabama Extension
Soil Compaction Stress and Trees - Dr. Kim Coder
USDA Web Soil Survey

ISA Standards and Best Management Practices - ISA store

   (3) Additional minimum soil quality requirements.  Soils used in landscape areas for tree planting must be shown on a landscape plan or a tree protection plan in protected zones where existing soil and vegetation is not disturbed or in zones modified to correct limiting factors for tree establishment and longevity.