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'~~ ~ ~ • • = III IIIIIIIIIIIIIIII <br />999 <br />c older <br />a Associates <br />February 27, 1997 <br />Mountain Coal Company <br />West Elk Mine <br />P.O. Box 591 <br />Somerset, Colorado 81434 <br />RE: WEST ELK MINE -SMALL AREA EXEMPTIONS (SAE) <br />SYLVESTER GULCH FACILITIES <br />Deaz Eric: <br />Our Ref: 963-2178 <br />This letter report describes the methods of analysis and results for five Small Area <br />Exemption (SAE) demonstrations pertaining to the Sylvester Gulch Facilities Project. <br />(Permit Revision 07 to Permit #C-80-007). The five SAE demonstrations include an <br />electrical substation and the cut slope above the substation, three topsoil storage piles, and <br />one area that includes both a topsoil pile and a subsoil pile. Topsoil Pile #5 is tributary to <br />existing Pond MB-1 thus no SAE for Topsoil Pile #5 was performed. These facilities are <br />shown on Map 53B and 54B and further described in Exhibit 69. <br />METHOD OF ANALYSIS <br />To qualify as a Small Area Exemption (SAE), runoff from disturbed ground must not exceed <br />effluent limitations during a 10-yeaz 24-hour storm event of 0.5 milliliters/liter (mill) of peak <br />settleable concentration (SSp) of sediment (reference Rule 4.05.2, Division of Minerals and <br />Geology). <br />All analyses were made using the Sediment, Erosion, Discharge by Computer Aided Design <br />(SedCAD+ Version 3) developed by Ms. Pamela J. Schwab of Civil Software Design and <br />Dr. Richard C. Warner, Agricultural Engineering Department, University of Kentucky. <br />Field information was provided by Eric Mende (Civil Engineer, Mountain Coa] Company). <br />For all sites, SedCAD+ soil input parameters include an overall classification as loam <br />(SedCAD+ classification of ordinary fum loam), K (a measure of susceptibility of soil <br />particles to detachment and transport by rainfall and runoff) soil erodibility equal to 0.32, <br />and a hydrologic group of C. The Storm Type was selected as SCS Type Il. The <br />SedCAD+ model time increment (hydrograph convolution interval) was selected as 0.1 <br />