Erosion prevention practices - tackifiers and soil stabilizers
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Contents
Tackifiers and Soil Stabilizers
Definition
Tackifiers and soil stabilizers are hydraulically applied chemicals derived from natural and synthetic sources used to promote adhesion among soil particles or mulch materials. In general, soil stabilizers (also known as soil binders) are used to increase soil adhesion, which improves soil stabilization by reducing water and wind driven erosion. Tackifiers are used as “glue” to bind and immobilize straw, cellulose products, pine needles, or other mulch that has been applied to a seeded area. Tackifiers protect seedbeds by holding the product to the soil surface and preventing movement. Relevant products include polyacrylamide, guar, chloride compounds, psyllium, resins, enzymes, surfactants, and various polymers, starches, and other compounds. Petroleum based tackifiers, once widely applied to straw mulch, have largely been replaced with other products that are easier to handle, break down naturally, and present fewer overall health and environmental risks.
Purpose and Function
Chemical based soil stabilization is intended to counteract the erosive influences of rainfall, snowmelt, and wind on bare soil. The use of tackifiers to prevent the movement of mulch material by wind and rain helps to keep straw and/or other mulches in place, preventing soil erosion. Erosion prevention practices are the easiest, cheapest, and most effective approach for addressing muddy runoff and dust from construction sites. Stabilizers and tackifiers are temporary measures, designed to prevent short-term (e.g., two to four weeks) erosion between construction periods, and during seed germination and early growth for permanent stabilization. While they are effective for a wide range of soil, slope, temperature, and rainfall conditions, they are not intended for use in concentrated flow locations, such as ditches and channels.
Applicability
Site stabilization with soil binders and tackifier bonded mulch (e.g., straw, other fibers) applies to 1) areas of construction sites where soil disturbing activities have temporarily ceased, and measures are needed to prevent erosion and sediment runoff during rainfall or snowmelt; and 2) areas of the site that require permanent stabilization.
Site Applicability
Construction sites often have areas where soil disturbing activities such as clearing, grading, or cut/fill work has stopped for a period of time. Bare areas that are not actively being worked need some type of cover or stabilization practice to prevent or minimize erosion in the event of rainfall or snowmelt. Tackifiers and soil stabilizers are applied hydraulically to reduce erosion by binding soil particles or mulch materials, often in conjunction with temporary or permanent seeding. Applicable areas include topsoil stockpiles, rough graded areas, sediment basin dikes, temporary earthen structures, and graded areas. Tackifiers and soil stabilizers can be used in conjunction with seed and mulch materials to achieve temporary and/or permanent stabilization.
Permit Applicability
The MPCA Construction General Permit has several requirements regarding temporary stabilization. Part IV.B.2 of the MPCA Construction General Permit states that the permittee(s) “must stabilize all exposed soil areas (including stockpiles). Stabilization must be initiated immediately to limit soil erosion whenever any construction activity has permanently or temporarily ceased on any portion of the site and will not resume for a period exceeding 14 calendar days.” In addition, “(s)tabilization must be completed no later than 14 calendar days after the construction activity in that portion of the site has temporarily or permanently ceased.”
Near public waters for which the Minnesota DNR has promulgated “work in water restrictions” during specified fish spawning time frames, all exposed soil areas that are within 200 feet of the water’s edge, and drain to these waters must complete the stabilization activities within 24 hours during the restriction period. Temporary stockpiles without significant silt, clay or organic components (e.g., clean aggregate stockpiles, demolition concrete stockpiles, sand stockpiles) and the constructed base components of roads, parking lots and similar surfaces are exempt from this requirement.
Other permit stabilization requirements relate to permanent stabilization and stormwater controls. For sites discharging to special or impaired waters, Appendix A Section C.1 of the MPCA Construction General Permit requires that (s)tabilization of all exposed soil areas must be initiated immediately to limit soil erosion but in no case completed later than seven (7) days after the construction activity in that portion of the site has temporarily or permanently ceased.”
As the permit notes, stabilization requires more than seed alone. Appendix B Section 26 of the MPCA Construction General Permit defines stabilization as meaning that “the exposed ground surface has been covered by appropriate materials such as mulch, staked sod, riprap, erosion control blanket, mats or other material that prevents erosion from occurring. Grass, agricultural crop or other seeding alone is not stabilization. Mulch materials must achieve approximately 90 percent ground coverage (typically 2 ton/acre).”
Effectiveness
Hydraulically applied products have undergone rapid development and improvement during the past ten years and now provide seed establishment and soil protection performance equal or superior to conventional seeding and mulching practices. Temporary and permanent stabilization with mulch-adhered tackifiers and soil stabilizers is effective in reducing soil loss from construction sites by increasing mulch longevity and preventing mulch displacement via wind and heavy rain. Tackifiers used as adhesives in hydraulically applied mulches (e.g., bonded fiber matrix, other hydromulches) have been used for decades, and provide results similar to rolled erosion control products in non-channel applications when selected, prepared, and applied in accordance with manufacturer’s directions. Chemical soil stabilizers bind the soil, helping it to further resist raindrop, sheet, and rill erosion. Soil stabilizers, when used as adhesives, are effective for dust control, short-term erosion prevention, and roadway stabilization. Some stabilizers, such as polyacrylamide, can be used as coagulants in sediment ponds to promote flocculation and settling. Table 3 1 summarizes expected performance for an array of typical water quantity and quality target constituents for tackifiers and soil stabilizers.
Expected performance for tackifiers and soil stabilizers.
Link to this table
| Water Quantity | |
|---|---|
| Flow attenuation | Little or no design benefit |
| Runoff volume reduction | Little or no design benefit |
| Water Quality | |
| Pollution prevention | |
| Soil erosion | Primary design benefit |
| Sediment control | Little or no design benefit |
| Nutrient loading | Primary design benefit |
| Pollutant removal | |
| Total suspended solids | Primary design benefit |
| Total phosphorus | Primary design benefit |
| Heavy metals | Secondary design benefit |
| Floatables | Little or no design benefit |
| Oil and grease | Little or no design benefit |
Planning Considerations
A key benefit of hydraulically applied products is the ability to treat large sites with steep (3H:1V to 1H:1V), long slopes or other areas where installation of ECBs or turf reinforcement mats is difficult. A nearby source of water (or water tank) to mix the slurry is necessary for large sites. Typical hydraulic soil cover applications include a slurry-like mix of seed, fertilizer, and mulch. Also available for inclusion are other amendments such as tackifier and a variety of fibrous materials that dry to form a flexible net or crust that provides excellent protection for bare soil before seed germination.
Application equipment ranges from small, hand-pulled polyethylene units with electric sprayers and tanks that hold up to 15 pounds of seed, fertilizer, and mulch, to large towed or truck-mounted machines with tanks of 100 to 2,000 gallons. Mixing ratios will vary significantly by application, but a standard turf application for one acre will typically include 100 to 150 pounds of seed (or more, depending on seed variety and site conditions), 300 to 400 pounds of fertilizer, 140 pounds of binder, and 1,500 to 2,000 pounds of fiber mulch mixed with 4,000 or more gallons of water.
As soil binder types (see Table 3 2 for MnDOT approved products) and uses have expanded in recent years, refer to the following when selecting a binder product:
- Soil types, slopes, and circumstances: What types of soils are present, how steep are they, and what is the slope length? Is the slope graded smooth or is it rough? Will the binder require resistance to leaching or abrasion? Is there existing vegetation to preserve? How long will the binder need to remain effective?
- Application: Is there sufficient water nearby to mix the product? Are the slopes accessible to the tank/sprayer equipment? Can the equipment effectively treat the area(s) under review? How frequently must applications be made? Are the manufacturer’s applications rates being followed?
- Product requirements: What are the required application conditions for the specific product under consideration – including soils, slopes, wetness/dryness, surface conditions (i.e., smooth/rough, compacted/loose, etc.)?
- Costs, equipment, and labor required for accessing, transporting, preparing, applying, and maintaining the product.
MnDOT approved/qualified hydraulic erosion prevention/control products
Below is summary information on some of the most widely used soil binders.
Binders from plant materials, lasting less than six months:
- Guar is a non-toxic, biodegradable, natural colloidal product treated with dispersant agents for easy field mixing. It should be mixed with water at the rate of 11 to 15 pounds per 1,000 gallons. Recommended minimum application rates range from 40 pounds per acre for flat areas to 70 pounds per acre for 1H:1V slopes.
- Psyllium is composed of the finely ground coating of plantago seeds, and is applied as a dry powder or in a wet slurry to the surface of the soil. Although it dries to form a firm but re-wettable membrane that binds soil particles together, it permits germination and growth of seed. Psyllium should be sufficiently mixed and diluted to provide uniform flow for application rates of 80 to 200 pounds per acre. Note that this product requires a 12 to 18 hour drying time prior to the next precipitation event.
- Starch is non-ionic, cold water soluble granular cornstarch mixed with water and applied at the rate of 150 pounds per acre. Approximate drying time is 9 to 12 hours.
Binders from plant materials, lasting six to twelve months:
- Pitch and rosin emulsions are manufactured from natural resins and generally have a minimum solids content of 48 percent. The rosin should be at least 26 percent of the total solids content, non-corrosive, dilutable, and cure to form a water insoluble binding and cementing agent. For soil