BMP Chapter 6-7-3.pdf

Pennsylvania Stormwater Best Management Practices Manual Chapter 6

BMP 6.7.3: Soil Amendment & Restoration ss of il or

Soil amendment and restoration is the proce improving disturbed soils and low organic soils by restoring soil porosity and/or adding a so amendment, such as compost, for the purpose of reestablishing the soil’s long-term capacity f infiltration and pollution removal.

Commercial:

Ultra Urban:

Industrial:

Retrofit:

Highway/Road:

Yes Yes Yes Yes Yes

Stormwater Functions

Volume Reduction:

Recharge:

Peak Rate Control:

W ater Quality:

Low/Med.

Low/Med.

Medium Medium

Water Quality Functions

TSS:

TP:

NO3:

85% 85% 50%

Existing soil conditions should be evaluated before forming a estoration strategy.

Physical loosening of the soil, often called subsoiling, or tilling, an treat compaction.

The combination of subsoiling and soil amendment is often the ore effective strategy.

Compost amendments increase water retention.

Key Design Elements Potential Applications

Residential: Yes r c m

363-0300-002 / December 30, 2006 Page 221 of 257

Problem Description nimals, farm equipment, trucks, construction quipment, cars, and people cause compaction. Wet oil compacts easier than dry soil. Natural compaction ccurs due to special chemical or physical properties, nd these occurrences are called “hard pans”. A pical soil after compaction has strength of about ile studies have shown that root growth not possible beyond 3,000 kPa.

Dif

2) Major Compaction – deep compaction, contact pressure and total load, axle load > 20 tons can

A e s o a ty 6,000 kPa, wh is ferent Types of Compaction

1) Minor Compaction – surface compaction within 8-12” due to contact pressure, axle load > 10 tons can compact through root zone, up to 1’ deep compact up to 2’ deep (usually large areas compacted to increase strength for paving and foundation with overlap to “lawn” areas)

In general, compaction problems occur when airspace drops to 10-15% of total soil volume.

mpactionCo affects the infiltrating and water quality capacity of soils. When soils are compacted, the ecessary to move air and water ase in bulk density (weight of solids per roo oil organisms are also affected by compaction; biological activity is greatly reduced, decreasing their bility to intake and release nutrients.

soil particles are pressed together, reducing the pore space n hroughout the soil. This decrease in porosity causes an incret unit volume of soil). The greater the bulk density, the lower the infiltration and therefore the larger olume of runoff. v

Different types of soils have bulk density levels at which compaction starts to limit root growth. When t growth is limited, the uptake of water and nutrients by vegetation is reduced.

S a

363-0300-002 / December 30, 2006 Page 222 of 257

The best soil restoration is the complete revegetation of woodlands, as “A mature forest can absorb as uch as 14 times more water than an equivalent area of grass.” (DNREC and Brandywine onservancy, 1997) (See Structural BMP 6.7.2 Landscape Restoration and use in combination with

Soil Restoration Methodology

Soil restoration is a technique that can be used to re organic content by physical treatment and/or mixture has been shown to alter soil properties known to affe capacity, porosity, bulk density and structure. Two m characteristics of soils that are damaged by compac compost or other materials.

One of the options for soil amendment is compost, which has many benefits. It improves the soil structure, creating and enhancing passageways in the soil for air and water that have been lost due to compaction. This recreates a better environment for plant growth. Compost also supplies a slow release of nutrients to plants, specifically nitrogen, phosphorous, potassium, and sulfur. Using compost reuses natural resources, reducing waste and cost.

Soil amendment with compost has been shown to increase nutrients in the soil, such as phosphorus and nitrogen, which provides plants with needed nutrients, reducing or eliminating the need for fertilization. This increase in nutrients results in an aesthetic benefit as turf grass and other plantings establish and proliferate more quickly, with less maintenance requirements. Soil amendment with compost increases water holding and retention capacity, improves infiltration, reduces surface runoff, increases soil fertility, and enhances vegetative growth. Compost also increases pollutant-binding properties of the soil properties, which improves the quality of the water passing through the soil mantle and into the groundwater.

The second method is tilling, which involves the digging, scraping, mixing, and ripping of soil with the intent of circulating air into the soil mantle in various layers.

Compaction down to 20 inches often requires ripping for soil restoration. Tilling exposes compacted soil devoid of oxygen to air and recreates temporary air space.

Bulk density field tests may be used to determine the compaction level of soils.

m C this BMP) store and enhance compacted soils or soils low in with additives such as compost. Soil restoration ct water relations of soils, including water holding ethods have been shown to restore some of the tion; tilling and addition of amendments such as

Soil Texture Ideal Bulk densities

Bulk densities that may afffect root growth

Bulk densities that restrict root growth g/cm3 g/cm3 g/cm3 Sands, loamy sands <1.60 1.69 1.8 Sandy loams, loams <1.40 1.63 1.8 Sandy clay loams, loams, clay loams <1.40 1.6 1.75 Slilt, silt loams <1.30 1.6 1.75 Silt loams, silty clay loams <1.10 1.55 1.65 Sandy clays, silty clays, some clay loams (35-45% clay) <1.10 1.49 1.58 Clays (>45% clay) <1.10 1.39 1.47

Source: Protecting Urban Soil Quality, USDA-NRCS

363-0300-002 / December 30, 2006 Page 223 of 257

Variations nd, and manufactured microbial solutions.

ave application time.

ntial, Commercial, Industrial) – new lawns can be amended with compost and not heavily compacted before planting, to increase the porosity of the soils.

soils that have been compacted before it is converted into meadow, lawn, or a stormwater facility is recommended.

• ntion basins is usually heavily compacted, and tilling the soil mantle on surfaces beyond the constructed embankment will encourage

• substitute for dwindling supplies of native topsoil in urban areas.

• Golf Courses – Using compost as part of the landscaping upkeep on the greens has been shown to alleviate soil compaction, erosion, and turf disease problems.

Design Considerations

1. Treating Compaction by Soil Restoration

a) Soil amendment media usually consists of compost, but can include mulch, manures, sand, and manufactured microbial solutions.

b) Compost should be added at a rate of 2:1 (soil:compost). If a proprietary product is used, the manufacturer’s instructions should be followed in terms of mixing and application rate.

c) Soil restoration should not be used on slopes greater than 30%. In these areas, deep-rooted vegetation can be used to increase stability.

d) Soil restoration should not take place within the drip line of a tree to avoid damaging the root in hes compost / amendment and till up to 20 inches for major compaction.

c) Ripping (Subsoiling) should be performed using a solid-shank ripper and to a depth of 20 inches, (8 inches for minor compaction).

• Soil amendment media can include compost, sa

• Seed can be included in the soil amendment to s

Applications

• New Development (Reside

• Urban Retrofits - Tilling of

Detention Basin Retrofits – The inside face of dete infiltration to take place. Tilling may be necessary to establish better vegetative cover.

Landscape Maintenance – compost can system.

e) On-site soils with an organic content of at least 5 percent can be properly stockpiled (to mainta organic content) and reused.

f) Procedure: rototill, or rip the subgrade, remove rocks, distribute the compost, spread the nutrients, rototill again.

g) Add 6 inches compost / amendment and till up to 8 inches for minor compaction.

h) Add 10 inc

2. Treating Compaction by Ripping / Subsoiling / Tilling / Scarification

a) Subsoiling is only effective when performed on dry soils.

b) Ripping, subsoiling, or scarification of the subsoil should be performed where subsoil has become compacted by equipment operation, dried out and crusted, or where necessary to obliterate erosion rills.

363-0300-002 / December 30, 2006 Page 224 of 257

d) Should be performed before compost is placed and after any excavation is completed.

e) Subsoiling should not be performed within the drip line of any existing trees, over und utility installations within 30 inches of the surface, where trenching/drainage lines are installed, whe erground re compaction is by design.

ubsoiling should not be performed with common tillage tools such as a disk or chisel plow because pact the soil just beneath the tillage depth.

be a cost-effective alternative that reuses waste materials.

d) In areas where compaction is less severe (not as a result of heavy construction equipment), ral

S they are too shallow and can com

3. Other methodologies:

a) Irrigation Management – low rates of water should be applied, as over-irrigation wastes water and may lead to environmental pollution from lawn chemicals, nutrients, and sediment.

b) Limited mowing – higher grass corresponds to greater evapotranspiration.

c) Compost can be amended with bulking agents, such as aged crumb rubber from used tires or weed chips. This can planting with deep-rooted perennials can treat compaction, however restoration takes seve years.

363-0300-002 / December 30, 2006 Page 225 of 257

Detailed Stormwater Functions

Infiltration Area (If needed) The f res e onditions, and the restoration effectiveness.

tion Calculations Soil Amendments can reduce the need for irrig io releasin rooting. Infiltration is increased; therefore the volu

Compost amended soils can significantly red e soils th accord BMP, or subject to restoration such that the field Bulk Densities of Table reduction may be applied:

Am eak Rate Mitigation

See improve in iltration area will be the entire area tor d, depending on the existing soil c

Volume Reduc at n by retaining water and slowly g moisture, which encourages deeper me of runoff is decreased.

uc the volume of stormwater runoff. For at have either been compost amended ing to the recommendations of their measured bulk densities meet the Ideal 1, the following volume n.

ended Area (ft2) x 0.50in x 1/12 = Volume (cf)

P See Section 8 for peak rate mitigatio

Water Quality Improvement

Section 8 for water quality ment.

363-0300-002 / December 30, 2006 Page 226 of 257

Co

1.

Maintenance Issues ction by use and/or ettling. (For example, playfields or park areas will be compacted by foot traffic.)

Cost I

Tilli

Com

Specifications

The following specifications are provided for information purposes only. These specifications include information on acceptable materials for typical applications, but are by no means exclusive or limiting.

The designer is responsible for developing detailed specifications for individual design projects in accordance with the project conditions.

1. SCOPE

a. This specification covers the use of compost for soil amendment and the mechanical restoration of compacted, eroded and non-vegetated soils. Soil amendment and restoration is necessary where existing soil has been deemed unhealthy in order to restore soil structure and function, increase infiltration potential and support healthy vegetative communities.

b. Soil amendment prevents and controls erosion by enhancing the soil surface to prevent the initial detachment and transport of soil particles.

2. COMPOST MATERIALS

a. Compost products specified for use in this application are described in Table 1. The product’s parameters will vary based on whether vegetation will be established on the treated slope.

b. Only compost products that meet all applicable state and federal regulations pertaining to its production and distribution may be used in this application. Approved compost products must meet related state and federal chemical contaminant (e.g., heavy metals, pesticides, etc.) and pathogen limit standards pertaining to the feedstocks (source materials) in which it is derived.

c. Very coarse compost should be avoided for soil amendment as it will make planting and crop establishment more difficult.

nstruction Sequence

All construction should be completed and stabilized before beginning soil restoration.

The soil restoration process may need to be repeated over time, due to compa s ssues ng costs, including scarifying sub-soils, range from $800/ac to $1000/ac.

post amending of soil ranges in cost from $860/ac to $1000/ac.

363-0300-002 / December 30, 2006 Page 227 of 257

d. Note 1 - Specifying the use of compost products that are certified by the U.S.

Composting Council’s Seal of Testing (STA) Program (www.compostingcouncil.org) will uisition of products that are analyzed on a routine basis, using the participants are also required to provide a standard product wing easy comparison to other products.

3. SUB-SOILING TO RELIEVE COMPACTION

is placed and preferably when excavation is completed, the e, friable condition to a depth of 20 inches below final topsoil ion rills or washouts in the subsoil surface exceeding 3

b. To achieve this condition, subsoiling, ripping, or scarification of the subsoil will be owners s representative, wherever the subsoil has been tion or has become dried out and crusted, and where ills. Sub-soiling shall be required to reduce soil e plant establishment is planned. Sub-soiling shall be avating contractor and shall occur before compost eas shall be loosened to less than 1400 kPa (200 psi) to a depth of 20 inches below final topsoil grade. When directed by the owner’s representative, the ork conforms to the specified depth.

g shall form a two-directional grid. Channels shall be created by a ulti-shanked, parallelogram implement (solid-shank ripper).

The equipment shall be capable of exerting a penetration force necessary for the site.

s chisel plows, or spring-loaded equipment will be allowed. The grid spaced a minimum of 12 inches to a maximum of 36 inches apart, depending on equipment, site conditions, and the soil management plan. The channel depth shall be a minimum of 20 inches or as specified in the soil management plan. If soils are saturated, the Contractor shall delay operations until the soil will not hold a ball when squeezed. Only one pass shall be performed on erodible slopes greater than 1 vertical to 3 horizontal. When only one pass is used, work should be at right angles to the direction of surface drainage, whenever practical.

e. Exceptions to sub-soiling include areas within the drip line of any existing trees, over utility installations within 30 inches of the surface, where trenching/drainage lines are installed, where compaction is by design (abutments, footings, or in slopes), and on inaccessible slopes, as approved by the owner’s representative. In cases where exceptions occur, the Contractor shall observe a minimum setback of 20 feet or as directed by the owner’s representative. Archeological clearances may be required in some instances.

4. COMPOST SOIL AMENDMENT QUALITY

a. The final, resulting compost soil amendment must meet all of the mandatory criteria in Table 4.

allow for the acq specified test methods. STA label to all customers, allo

a. Before the time the compost subsoil shall be in a loos grade and there shall be no eros inches in depth.

required as directed by the compacted by equipment opera necessary to obliterate erosion r compaction in all areas wher performed by the prime or exc placement.

c. Subsoiled ar

Contractor shall verify that the sub-soiling w

d. Sub-soilin commercially available, m

No disc cultivator channels shall be

363-0300-002 / December 30, 2006 Page 228 of 257

5. COMPOST SOIL AMENDMENT INSTALLATION

sting soil with a rotary tiller that is set to a depth of 6 inches. Add an additional 4 inches of ompost to bring the area up to grade.

ll ction Techniques, Article 36, 3(2): 661-665.

allas, H. and A. Lewandowski, 2003. Protecting Urban Soil Quality: Examples for Landscape Codes and Specifications. USDA Natural Resources Conservation Services.

CSCD, 2001. Impact of Soil Disturbance During Construction on Bulk Density and Infiltration in

a. Spread 2-3 inches of approved compost on existing soil. Till added soil into exi approved c

b. After permanent planting/seeding, 2-3 inches of compost blanket will be applied to a areas not protected by grass or other plants

References

“The Compaction of Urban Soils”, Technical Note #107 from Watershed Prote

D

O

Ocean County, New Jersey. Ocean County Soil Conservation District, Schnabel Engineering Assoicates, Inc., USDA Natural Resources Conservation Services. www.ocscd.org.

Pitt, R. et al., 2002. “Compacted Urban Soils Effects on Infiltration and Bioretention Stormwater Control

Designs.”

Pitt, R. et al., 2002. “Infiltration Through Disturbed Urban Soils and compost-Amended Soil Effects on

Runoff a

“The Relations

“Soil Quality R ction”, USDA Natural Resources Conservation Service, 1996

“Soil Quali

Service, 19

“Sp ts”, Low Impact Development Center, Inc., www.lid-

Qu lity and Quantity.”

hip Between Soil and Water”, Soils for Salmon, The Urban Environment, 1999 esource Concerns: Compa ty Resource Concerns: Available Water Capacity”, USDA Natural Resources Conservation ecifications for Soil Amendmen stormwater.net/soilamend/soilamend_specs.htm

“Urban Soil Co

Conservation Services, 2000.

Department of t and Sedim mpaction”, Soil Quality – Urban Technical Note, No. 2, USDA Natural Resources

Na ural Resources and Environmental Control Division of Soil and Water. Delaware Erosion ent Control Handbook for Development. Newark, DE

363-0300-002 / December 30, 2006 Page 229 of 257

363-0300-002 / December 30, 2006 Page 230 of 257