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p Jill <br />IA <br />• •.• .. -TRIM-79-11liM 71,11J11L At <br />The surface soils present at the site are susceptible to erosion, particularly when disturbed by <br />construction activities. Surface runoff will typically sheet flow in areas of uniform slopes, but will <br />be concentrated where undulations occur. Concentrations of surface flows can rapidly cut down <br />through the soil and promote slope instability. Temporary erosion control measures must be used <br />during construction to limit the damage that would result during precipitation events. For the <br />long-term, erosion can be controlled on uniform slopes by the growth of grasses and other <br />vegetation. In concentration areas, erosion may be controlled in the long-term by the <br />implementation of drainage control structures. <br />Mitigation <br />4.4-5 Erosion control measures shall be implemented, during construction and project operation. <br />Options for erosion control can include: <br />• Placement of plastic sheeting, debris fences, silt fences, and/or hay bales to protect <br />disturbed surfaces during precipitation events that occur during construction. <br />• Following construction, all disturbed surfaces, especially on slopes, would be seeded with <br />an appropriate dry land erosion control seed mix and covered with hand -spread straw. <br />Drainage control structures such as ditches, curbs and gutters, and down -drains would <br />be constructed in drainage concentration areas. <br />ER -93-1 -63- (9-27-93) <br />