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Small Area Exemptions <br />• Topsoil Stx]cpila: Thera are currently three topsoil stockpiles within the permit area. Two of <br />the piles and a portion of the third do not drain to sad- t ponds. In order to ~~+^~trate <br />that these piles meat the intention of CDI~ Regulation, Section 4.05.2(3), SEDCAD+ analyses were <br />conducted. These computer analyaie can be found in ar.~^.+~ 12-2. <br />The statue of the piles has not changed ainw their construction in the late 1970's axoept for <br />vegetative cover. A similaz demonstration was made by ColoWyo Coal Company for the topsoil <br />stockpiles at the H~ minesite (approved Permit C-SO-003). Many of the pazametera used in those <br />demonstrations have been borrowed for this exercise based on aimilaz seeding dates, rates, etc. <br />Due th the shallow slopes, vegetation cover, and small dra;^~ area. None Of the stockpiles <br />exhibit a soil loss through sediment erosion. <br />The following briefly describes the input and output from those SEDCAD+ analysis. <br />Input Su®ary <br />10-yr. 24-hr Precipitation 1.6 in. <br />CN Factor 48 <br />R Factor 0.25 <br />• CP Factor 0.075 <br />Output Summary <br />Ihinoff Volumes and ~~+~^t <br />Topsoil Pila 1 0.0 <br />Topsoil Pile 2 0.0 <br />Topsoil Pile 3 0.0 <br />Substation: Thera is ~ *+~^tly a substation located in the northwest corner of the loadaut area <br />ae shown in Exhibit 12-2. The substation is surrounded by a 30 by d0 foot area xtiich ie graveled <br />and fenwd. Also associated with the substation is some additional disturbed area outside the <br />fenwd area. Runoff from the substation area does not drain to the axiating serL_ t pond and <br />will be controlled wing a sediment fanw. The location of the sediment fenw is shown on <br />Exhibit 12-2. The sediment fenw is designed to safely pass the peak dieclmrgB from a 10-year, <br />24-hour avant. All deeigna can be Found in r~ ~;. 12-2 Small Area Exertion SEDCAD+ <br />Information. Given the limited size of the diaturbanw area and the use of a sediment fenw HGT <br />respectively requests a Small Area Exemption for the substation area. <br /> <br />iPN-o l <br />1 Revised 10/97 <br />