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• l) an existing watershed runoff interceptor ditch, Ditch D-1, above the pile. It is designed to divers <br />runoff from a 100-yeaz, 24-hour storm. Ditch D-1 is a parr of this demonstration, however the design <br />and analysis ojDirch D-1 is part ojother SAE demonstrations (Fan Bench, Staging Area, and Topsoil <br />Stockpile). <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) azound the upper portions of the pile. Runoff <br />from the upper half of the pile would be divided and flow azound the toe-of-slopes in these ditches. <br />These ditches would also capture runoff from small watersheds located between the interceptor ditch <br />(Ditch D-I) and the circumvential ditches. These circumvential ditches will be feathered out inside <br />(uphill) of the perimeter silt fence to distribute dischazge along portions of the lower silt fence (and <br />thence into vegetative debris filters). These ditches will be constructed prior to any placement of waste <br />on the pile. During construction, entrenchment of these ditches will be arrested by the exposure and <br />accumulation of the cobble sized fraction of the site soils. Aher construction (no more development <br />waste to be placed on the pile), these circumvential ditches will be seeded and protected with mulch. <br />These circumvential ditches aze designed to accommodate 100-yeaz, 24-hour storm events. <br />~ after construction is complete, the pile and dismrbed areas about the site will be stabilized with <br />vegetation (seeding and mulched). <br />5) natural vegetation and vegetative debris ground litter (equated to a grass filter). Runoff from the <br />downhill slopes of the pile and dischazge from the circumvential ditches would flow through the lower <br />silt fence and into the vegetative debris filter. The filter will provide final filtration of all the twtoff <br />• from the pile. <br />This analysis addresses a "worst case" scenario, i.e., the site is protected by an interceptor ditch, the circumvential <br />ditches have not been vegetated, and the entire pile is considered as constructed with no ground cover. No credit <br />is given to silt fences or straw bales with regard to sediment control or mitigation of affects on the quality of storm <br />runoff. Partial implementation of all the best management practices identified will reduce the potential for erosion <br />and 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 dismrbed ground must not exceed effluent limitations <br />during a ]0-yeaz 24-hour storm event of 0.5 milliliters/liter (ml/1) of peak settleable concentration (SSp) of sediment <br />(reference Rule 4.05.2, Division of Minerals and Geology). Thus water quality analyses are based on this storm <br />event. <br />The development waste pile is to be protected from 100-yeaz, 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 freeboazd for diversion ditches is required by the Division of Minerals and Geology [Rule 4.05.3(7)]. <br />A 0.5 foot of freeboazd is used for to design for all the ditches, however, to add an extra measure of protection. <br /> <br />(West Elk Lone Pine Gulch Developmem Waste Pile SAE. 12 October 1995, Page 2 of 7) <br />