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• Mr. Crellin Scott <br />July 30, 2002 <br />Page 3 of 3 <br />100-year, 6-hour amount. The SEDCAD 4 analysis indicates the peak elevation will <br />approach to within 2.47 feet of the top of the embanktnent without overtopping. <br />Based on the information provided by Colowyo Coal Company, the West Pit Pond meets <br />the (SCS) TR-60 classification criteria for a Class A Dam. The pond is located in an agricultural <br />area where failure is limited to damaging farm buildings, agricultural land, or county roads. <br />However, the dam classification system considers several factors that are objective (Earth Dams <br />and Reservoirs. Technical Release No. 60, Page 1-I). For exatnple, consideration is given for <br />existing and future development and the effect of failure on public confidence. Future <br />development in the mountains of Colorado is difficult to predict. Dams are classified as Class B <br />Dams if failure may damage isolated homes, main highways or railroads or interrupt service of <br />relatively important public utilities. <br />As a Class A structure, the West Pit Pond is not necessarily required to meet the TR-60 <br />Emergency Spillway Evaluation and the TR-60 Emergency fSpillway Freeboard Evaluation <br />conditions (items 11 and 12 above). However, the SEDCAD 4 models demonstrate that the West <br />. Pit Pond meets the criteria for a Class B structure. ' <br />Sincerely, <br />~.~ ~~/ <br />Steve Linse, <br />Colorado P.E. 35009 <br />Project Engineer <br />SL:sb <br />Enclosures <br />cc: Dale Brown <br />File: 99-642 <br />• <br />W <br />wC Engineering <br />