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..~ <br />vegetative areas. This ditch will be seeded and lined with a mulch mat. It will be constructed <br />(including seeding) prior to any placement of development waste on the pile. <br />2) a silt fence below the pile. This fence will be constructed prior to any placement of development <br />waste on the pile. <br />3) circumvential ditches (ditches DWP-W and DWP-E) around the upper portions of the pile. <br />Runoff from the upper half of the pile would be divided and Oow around the toe-of-slopes in <br />these ditches. These ditches would also ppture runoff from small watersheds located between <br />the interceptor ditch and the circumvential ditches. These circumvential ditches wilt be feathered <br />out inside (uphill) of the perimeter silt fence to distribute discharge ~Iong portions of the lower <br />silt fence (and [hence into vegetative debris filters). These ditches will be constructed prior to <br />any placement of waste on the pile. During construction, entrenchment of these ditches will be <br />arrested by the exposure and accumulation of the cobble sized fraction of the site soils. After <br />construction (no more development waste to be placed on the pile), these circumvential ditches <br />will be seeded and protected with mulch mats. These circumvential ditches are designed to <br />accommodate 100-vear, 24-hour storm events. <br />4) after construction is complete, a midslope silt fence will be placed on the downhill slopes of the <br />pile. <br />5) after construction is complete, the pile and disturbed areas about the site will be stabilized with <br />vegetation (seeding and mulched). <br />6) natural vegetation and vegetative debris ground litter (equated to a grass filter). Runoff from the <br />downhill slopes of the pile and discharge from the circumvential ditches would Oow through the <br />lower silt fence and into the vegetative debris filter. The filter will provide final filtration of all <br />the runoff from the pile. <br />This analysis addresses a "worst case" scenario, i.e., the site is protected by an interceptor ditch, the <br />circumvential ditches have not been vegetated, the entire pile is considered as constructed with no ground <br />cover, and only a lower perimeter silt fence is considered as installed. No credit is given to silt fences or straw <br />bales with regard to sediment control or mitigation of affects on the quality of storm runoff. Partial <br />implementation of all the best management practices identified will reduce the potential for erosion and <br />provide a degree of impact somewhat less than the 'worst case" scenario. <br />1.3 Criteria <br />To qualify as a Small Area Exemption (SAE), runoff from disturbed ground must not exceed effluent <br />limitations during a 10-year 24-hour storm event of 0.5 milliliters liter (ml/l) of peak settleable concentration <br />(SSp) of sediment (reference Rule 4.05.2, Division of Minerals and Geology). Thus water quality analyses are <br />based on this storm event. <br />The development waste pile is to be protected Crom 100-year, 24-hour, storm events [Rules 4.10.3(2) and <br />4.09.2(7)]. The interceptor and circumvential ditches are designed to provide this level of protection. <br />A 0.3 foot of Freeboard for diversion ditches is required by the Division of Minerals and Geology [Rule <br />4.05.3(7)]. A 0.5 foot of freeboard is used for to design for all the ditches, however, to add an extra measure <br />of protection. <br />(West Elk SAE. Lone Pine Gulch Devclopmem Waste Pite, Pape 2 0( 81 <br />