2012-10-05_REVISION - M1977342 (14)

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Climax Molybdenum Company HENDERSON MINE & MILL SWMP Empire & Parshall, CO December, 2011 Page 5-2 • Reseed disturbed soil areas with maintenance seed (if it is temporary) or Climax Seed Mix (for permanent or final construction). • Install mulch, excelsior blankets or reseed areas on disturbed slopes greater than 3:1 and consideration should be given to installation on slopes between 5:1 and 3:1 on a case by case basis depending on the length, exposure, and texture of the soils on the slope. • Avoid slopes steeper than 2:1 and when unavoidable, rock protection (riprap) or excelsior mats with netting shall be installed. • Install rip-rap and at least 6-inches of suitable bedding in all water flow channels where the design flow will exceed ~2 feet per second. Generally, suitable bedding ranges from a minimum diameter of sand to a maximum diameter of 2-3 inches of coarse, granular soils. • Furrow contour side hill slopes whenever suitable equipment is available. Otherwise, final grading shall be performed in a manner that will result in tracks and depressions contoured across the slope instead of a down “fall-line.” This will not only minimize wind erosion, but will also “roughen” the earth to provide a microclimate of wind protection for new plants, and will help conserve precipitation for use in growth of new seed. • Minimize the time that bare soil is exposed. • Install check dams and water bars wherever the slope exceeds approximately two percent (~2%) to reduce water velocities and erosion potential in constructed swales and channels. Riprap linings shall be installed in steeper slopes or where the velocity exceeds two (2) feet per second. • Minimize the disturbance of existing vegetation. • Reseed and apply mulch as soon as possible to disturbed areas where erosion is probable. Mulch may be natural, consisting of slash, brush, manure and vegetation previously chipped and stockpiled; and/or clean straw, free from noxious weed seed, mold, and other harmful elements; or wood cellulose fiber. • Apply erosion control mats to all cut slopes steeper than 3:1. Staples shall be installed at a maximum spacing of 4 feet. Mats shall overlap on the ends and sides at least 6 inches. Regular duty excelsior mats shall be used for slopes less than 2:1. Heavy duty excelsior or jute mats shall be used for slopes greater than 2:1. • Where erosion scarps have developed (particularly along the faces of flood detention structures), loose granular material shall be removed and the scarp filled with suitable soils to the original profile of the bank or slightly above the original profile. If the scarp is not completely filled, the steeper area at the brow of the scarp will encourage erosion and may cause redevelopment of the scarp. The area upstream from the scarp shall be carefully inspected to determine if there was an irregularity in the ground profile that caused storm water to concentrate and erode the soils. Any such irregularity shall be removed by the most appropriate BMP listed herein. • Cover soils known to have a relatively high erosion potential with coarser textured erosion resistant soils and mulch/reseed the topsoil. • Where feasible, bypass live stream flows around construction sites during earthwork activities by installation of temporary (or permanent) pipes or rock lined ditches.