P7.3: Restore Soils Disturbed by Construction – Above Green

Required

INTENT

Support healthy plants, biological communities, water storage, and infiltration by restoring soils disturbed during construction.

REQUIREMENTS

Restore all soils on site that have been disturbed by current construction activities and that will serve as the final vegetated area (regardless whether the pre-construction soil condition was classified as healthy or disturbed):

Locate reference soils to guide performance criteria that are appropriate for the site’s vegetation, intended program, and site elements.
- If identified reference soils are not appropriate for the design intent, explain why and describe the soil characteristics that will guide soil restoration treatment efforts. (See Pre-Design P2.2: Conduct a pre-design site assessment and Soil+Veg P4.1: Create and communicate a soil management plan.)
Restore soils to a minimum depth of 12 inches (30.48 centimeters).
- Where planting trees, restore soils to a greater depth and volume to support (biologically, structurally, hydrologically, and geotechnically) the intended mature tree canopy.
Test restored (final) soil conditions to ensure the following soil restoration criteria are met:

1. Organic matter (required):

Achieve appropriate organic matter for plant growth, water storage, and infiltration. Amend soils with mature, stable compost such that, at minimum, the top 12 inches of soil (30.48 centimeters) contain at least three percent organic matter or organic matter levels and depths that are comparable to the site’s reference soil and appropriate for vegetation and program needs. Do not use sphagnum peat or organic amendments that contain sphagnum peat.
Acceptable test methods for determining soil organic matter include the most current version of ASTM D2974 Test Methods for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils and TMECC 05.07A Loss-On-Ignition Organic Matter Method.

2. Compaction (field test or undisturbed core sample only):

Ensure bulk densities within 100 percent of the root zone do not exceed the maximum values given in Figure 7.3-A or Figure 7.3-B in the Documentation guidance section of the SITES v2 Reference Guide.

Infiltration (field test only):

Achieve infiltration rates (inches or centimeters per hour) or saturated hydraulic conductivity (millimeters per second) comparable to the site’s reference soils and appropriate for vegetation and program needs.

Note: This test must only be done in the field.

3. Soil chemical characteristics:

Restore appropriate soil chemical characteristics for plant growth. The minimum basic profile that must be tested includes:
- pH
- Soluble salts (electrical conductivity)
- Cation exchange capacity (CEC)
- Extractable phosphorus
- Potassium
- Calcium
- Magnesium
- Sodium (in semi-arid and arid climates)
The pH, cation exchange capacity, and nutrient profiles should be comparable to the original undisturbed soil or the site’s reference soil and appropriate for vegetation and program needs. Salinity must be suitable for regionally appropriate plant species.

Soil biological function:

Ensure that soil biological function is restored in remediated soils. Soil biota assays are complex and vary regionally, making potentially mineralizable nitrogen serve as a proxy assessment of biological activity.

Required tests per project area:

Restored Vegetated Area	Minimum Number of Soil Tests Required
≤ 0.5 acre (0.20 hectares)	1 set for each soil restoration treatment zone type (see Soil+Veg P4.1)
> 0.5 acre (0.20 hectares) to ≤ 1 acre (0.40 hectares)	2 sets for each soil restoration treatment zone type
> 1 acre (0.40 hectares) to 2 acres (0.81 hectares)	3 sets for each soil restoration treatment zone type
> 2 acres (0.81 hectares) to ≤ 20 acres (8.09 hectares)	1 set per acre for each soil restoration treatment zone type
> 20 acres (8.09 hectares)	1 set per 3 acres for each soil restoration treatment zone type

Note: If multiple soil restoration treatment zones have the same soil restoration methods, treat them as one type.

Structural or engineered media:

These specialized media are exempt from meeting the soil restoration criteria above when used for applications such as the following. However, all other requirements must be met and documentation submitted accordingly:

Athletic fields
Green roofs
Raingardens
Vertical green walls
Trees in paving
Bioswales
Green vehicle easements
Steep slopes
Food gardens
Constructed wetlands

Note: Neither imported topsoils nor manufactured soil blends designed to serve as topsoil may be mined from the following locations (unless soils are a byproduct of a construction process):

Greenfield sites
Prime farmland, unique farmland, farmland of statewide importance or farmland of local importance, as defined by the U.S. Natural Resources Conservation Service (or local equivalent for projects outside the United States)

RECOMMENDED STRATEGIES

Limit disturbance during construction to minimize the need for additional restoration. In areas that will be re-vegetated, restore soil characteristics necessary to support the selected vegetation types. Below are sample methods to restore soils:
- Stockpiling and reusing existing site topsoils, incorporating organic amendments, if needed
- Amending site soils in place with organic matter and mechanically correcting compaction if needed (e.g., by ripping or discing)
- Importing a topsoil or soil blend designed to serve as topsoil, avoiding prime farmland sources or greenfield sites unless soils are a byproduct of a construction process
When selecting a soil restoration strategy, consider the design, site use, and future site maintenance expectations. Consider the following possibilities:
- Adding mature, stable compost to unscreened soil can be a sustainable strategy.
- Many un-screened and un-amended soils will drain adequately.
- Amend with other earth materials to modify a soil’s gradation, texture, and organic matter content.
Select organic materials for on-site amendment or for blending of imported soils from sources that are renewable within a 50-year cycle:
- Mature, stable compost is recommended as the best source of organic matter, for its stability, biological activity, and soil structure building qualities. If mature, stable compost is not locally available, look for locally available organic residuals that can be composted on or off site to produce a mature composted organic amendment.
- Involve a qualified horticultural or soil professional in selecting and balancing amendments for healthy plant growth.
Guidelines for compost include these qualitative measurements:
- Has a carbon to nitrogen ratio (C:N) below 25:1. Higher C:N ratios may be acceptable if specified by a qualified professional to be more appropriate for the type of vegetation to be established.
- Does not exceed pollutant concentration limits established by the U.S. EPA in the 40 CFR Part 503 Biosolids Rule, section 503.13 table 3 “Pollutant Concentrations” (or local equivalent for projects outside the United States) or any applicable state or local regulations
- Does not contain viable weed seeds or invasive plant propagules
- Results in final soil conditions conducive to growing the type of vegetation to be established
Before placing stockpiled or imported topsoils, consider scarifying any areas of construction-compacted subsoil, except where this process will damage existing tree roots. Ideally, the first lift of replaced soil is mixed into this scarification zone in order to improve the transition between the subsoil and overlying soil horizons.

Required

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