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.