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Exh. 7-23M-2 Revision Date: 4/28/22 <br /> Revision No.: TR-154 <br />as riprapped when in fact only a very small portion on a steep slope contains riprap. The lower <br />portions of these channels are erodible structures. <br /> <br />Colowyo also has two small concrete sumps and a small concrete channel (less than 1 foot wide) <br />that are utilized to collect coal fines and route the settle out water to the Coal Stockpile Pond. <br />These two structures were not modeled to add another layer of conservatism into the model by <br />removing the retention time both structures provide. <br /> <br />In summary, for the Coal Stockpile Pond, the 100-year, 24-hour storm produces 6.54-acre feet of <br />runoff. The entire storm event is contained within the pond below the emergency spillway <br />elevation of 7217’.