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Mr. Crellin Scott <br />July 30, ?002 <br />Page 3 of 3 <br />the 100-year, 6-hour amount. The SEDCAD 4 analysis indicates that the routed peak <br />discharge during this event would overtop the embankment by 0.76 feet. <br />Based on the information provided by Colowyo Coal Company, the East Taylor Pond <br />meets the (SCS) TR-60 classification criteria for a Class A Dam. The pond is located in an <br />agricultural area where Failure is limited to damaging farm buildings, agricultural land, or county <br />roads. However, the dam classification system considers several factors that are objective (Earth <br />Dams and Reservoirs, Technical Release No. 60, Page 1-1). For example, consideration is given <br />for 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 East Taylor Pond is not necessarily required to meet the TR- <br />60 Emergency Spillway Evaluation and the TR-60 Emergency Spillway Freeboard Evaluation <br />conditions (items 11 and 12 above). However, the SEDCAD 4 models demonstrate that the East <br />Taylor Pond fails to meet the criteria for a Class B structure because the embankment will <br />overtop by 0.76 feet during the TR-60 Emergency Spillway Freeboard storm event. If Colowyo <br />Coal Company wants to meet the Class B structure criteria, the East Taylor embankment must be <br />raised by a minimum of 0.76 feet or the spillway must be expanded from 20 feet wide to 40 feet <br />wide. <br />Sincerely, <br />l <br />i / <br />Steve Linse, <br />Colorado P.E. 35009 <br />Project Engineer <br />SL:sb <br />Enclosures <br />cc: Dale Brown, w/enclosures <br />File: 99-6=42 <br />• <br />W <br />WC Engineering <br />