Laserfiche WebLink
_17_ <br />The proposed sediment pond for the underground development waste disposal pile <br />is designed for a total capacity of .185 acre-feet. This will allow for the <br />detention of the volume of runoff from the 10-year, 24-hour event (.12 <br />acre-feet) in addition to a three-year accumulation of sediment from the <br />disposal pile (.062 acre-feet). A sediment clean out marker must be installed <br />which indicates the level at which sufficient storage remains in the pond for <br />both runoff and sediment generated by the 10-year, 24-hour storm event. <br />The collector ditch for the pond at the underground development waste disposal <br />site will be stable under flows form the 10-year, 24-hour event and the <br />emergency spillway will be stable during flows resulting from the 25-year, <br />24-hour event. As in the case for the pond at the mine bench, the permit <br />application has been amended in response to the original CMLRD stipulation No. <br />2 to include provisions for installation of a dewatering device to dewater the <br />pond down to the maximum sediment storage level. <br />Central Facilities Area Sediment Pond <br />The proposed pond at the central facilities area is designed to hold a volume <br />of runoff and sediment of 5.53 acre-feet. this capacity allows for the <br />storage of runoff from two 10-year, 24-hour storm events (3.5 acre-feet) as <br />well as storage of 5 years volume of sediment accumulation (.145 acre-feet). <br />The Division requires that a sediment clean out marker be installed in the <br />pond to indicate the maximum level at which sufficient storage remains for <br />both runoff and sediment generated by the 10-year, 24-hour storm event. <br />Central Facilities Topsoil Stockpile Sediment Pond <br />The proposed pond at the central facilities topsoil stockpile is designed to <br />hold a volume of runoff and sediment of 0.3 acre-feet. This capacity allows <br />for the storage of runoff from one and one-half 10-year, 24-hour storm events <br />(.20 acre-feet) as well as storage of three years volume of sediment <br />accumulation (.10 acre-feet). The Division requires that a sediment clean out <br />marker be installed in the pond to indicate the maximum level at which <br />sufficient storage remains in the pond for both runoff and sediment generated <br />by the 10-year, 24-hour storm event. <br />The collector ditch into the pond will be stable under the flow from the <br />10-year, 24-hour storm event. The emergency spillway is designed to convey <br />flow from the 25-year, 24-hour event without eroding. Due to the small size <br />and incised nature of this pond, dewatering will be accomplished through the <br />use of a pump once the water quality meets or exceeds effluent standards. <br />Coal Processing Waste Disposal Area Sediment Pond <br />The proposed pond at the coal processing waste disposal area is designed to <br />hold a volume of runoff and sediment of 3.95 acre-feet. This capacity allows <br />for the storage of runoff from two 10-year, 24-hour storm events (1.95 <br />acre-feet) as well as storage of 6.7 years volume of sediment accumulation <br />(1.90 acre feet). During the review of the permit revision application it was <br />