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Other permit requirements exist during the construction of post-construction/permanent stormwater and temperature control BMPs discharging to special waters and impaired waters. In those cases, [http://stormwater.pca.state.mn.us/index.php/APPENDIX_A 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.”
 
Other permit requirements exist during the construction of post-construction/permanent stormwater and temperature control BMPs discharging to special waters and impaired waters. In those cases, [http://stormwater.pca.state.mn.us/index.php/APPENDIX_A 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.”
  
4.4. Effectiveness
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===Effectiveness===
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ECBs are effective in reducing rill, sheet, and wind erosion of bare soil on a range of situations, including slopes, swales, ditches, channels, and shore areas. Although their erosion reduction performance is generally 90 percent or more, their ultimate effectiveness is dependent upon the quality of surface preparation, installation methods (i.e., soil contact, staking pattern), and site conditions (e.g., slopes, soils, rainfall, etc.). Table 4 1 summarizes expected performance for an array of typical water quantity and quality target constituents for erosion control blankets.
 
ECBs are effective in reducing rill, sheet, and wind erosion of bare soil on a range of situations, including slopes, swales, ditches, channels, and shore areas. Although their erosion reduction performance is generally 90 percent or more, their ultimate effectiveness is dependent upon the quality of surface preparation, installation methods (i.e., soil contact, staking pattern), and site conditions (e.g., slopes, soils, rainfall, etc.). Table 4 1 summarizes expected performance for an array of typical water quantity and quality target constituents for erosion control blankets.
  
[[Expected performance for erosion control blankets]]
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Erosion Control Blankets

Definition

Erosion control blankets (ECBs) are typically biodegradable, open-weave blankets that provide temporary cover and support for establishing vegetation on bare soil areas.

Purpose and Function

ECBs provide cover for bare soil and support for emergent vegetation (i.e., typically grass) from the time of seeding until root density and top growth are capable of long-term erosion protection. ECBs function by shielding bare soil and newly seeded areas against raindrop and wind erosion, providing a dense matrix of biodegradable material (e.g., straw, coconut) that stabilizes and supports emergent vegetation and later decomposes to further aid in plant growth. They also help to increase precipitation infiltration and decrease soil crusting and compaction. ECBs are designed and fabricated in a variety of types that last from a few months to approximately three years. Temporary ECBs are grouped into categories based on functional longevity and according to the Erosion Control Technology Council (see Table 4 2) include:

Category 1: Ultra short-term – typically 3 months
Category 2: Short-term – typically 12 months
Category 3: Extended term – typically 24 months
Category 4: Long-term – typically 36 months

Applicability

Degradable ECBs are appropriate for any bare soil area where temporary protection from raindrop and wind erosion is needed, or where newly seeded grass requires short-term cover and support prior to germination, early growth, and full establishment.

This picture shows an erosion control blankets being installed along a steep slopeErosion control blankets being installed along a steep slope

Site Applicability

ECBs are typically used where vegetation requires only temporary support for establishment, such as flat upland areas and slopes less than 4H:1V. They are also effective in establishing vegetation on relatively flat shoreline areas, swales, ditches, and athletic fields, or grassy areas that will be mowed closely such as places where longer term plastic netting may cause a tripping hazard or be pulled up later by equipment. ECBs can also be used as temporary cover for small bare areas that are idle for a few weeks (i.e., time periods too long to remain unprotected, but too short to seed). In these cases, blankets can be unrolled on bare portions of the site for a short period, removed when work commences, and reused.

ECBs can be especially useful for establishing permanent vegetation on slopes 2H:1V or greater (Figure 4 1). They are generally effective for slopes up to 1.5H:1V, but may be used for slopes as steep as 1H:1V (see Table 4 2 for example specifications). Manufacturer specifications should be consulted to verify that the selected ECB is appropriate for the site’s slope conditions.

Permit Applicability

The MPCA Construction General Permit has several requirements regarding temporary stabilization – which means 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” (Appendix B Section 26). In addition, ECBs generally meet the requirement that mulch materials “achieve approximately 90 percent ground coverage.”

ECBs provide a quick, effective, and economical approach for stabilizing areas that need very short-term protection – for a few weeks or months, where temporary seeding may not be warranted. Part IV.B.2 of the MPCA Construction General Permit states that the permitte(s) “must stabilize all exposed soil areas (including stockpiles),” and notes that “(s)tabilization 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, the permit requires that “(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 requirements exist during the construction of post-construction/permanent stormwater and temperature control BMPs discharging to special waters and impaired waters. In those cases, 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.”

Effectiveness

ECBs are effective in reducing rill, sheet, and wind erosion of bare soil on a range of situations, including slopes, swales, ditches, channels, and shore areas. Although their erosion reduction performance is generally 90 percent or more, their ultimate effectiveness is dependent upon the quality of surface preparation, installation methods (i.e., soil contact, staking pattern), and site conditions (e.g., slopes, soils, rainfall, etc.). Table 4 1 summarizes expected performance for an array of typical water quantity and quality target constituents for erosion control blankets.

Expected performance for erosion control blankets
Link to this table

Water Quantity
Flow attenuation Little or no design benefit
Runoff volume reduction Little or no design benefit
Water Quantity
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