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C-.1J <br />.7 <br />E I <br /> Drainage Area, Acres Ditch Flow, cfs <br />Time frame August 10 model Current model August 10 model Current model <br />2010 53.9 ac 60.6 ac 0.68 cfs 2.69 cfs <br />2012 63.4 ac 70.1 ac 1.28 cfs 2.00 cfs <br />2017 77.1 ac 83.8 ac 1.64 cfs 2.00 cfs <br />The change in tributary acreage is simply the 6.7 acres of the new subdivided sub- <br />watersheds E1 and F2 that are now assumed to report into Structure 8 as opposed to <br />reporting just below it. In that regard, the total acreage of the watershed reporting to <br />structures downstream of this point has not changed. <br />While it can be observed that the flows in Structure 8 have changed, primarily because <br />these 6.7 acres of the 23.9 acres of adjacent watershed now report through Structure 8, the <br />flows are still very small in comparison to the capacity of the ditch, and they have no impact <br />on its design. <br />Should you have any questions or require additional information, please feel free to contact <br />me at (970) 824-1578. <br />Sincerely, <br />Ryan Pawlowski <br />Environmental Engineer <br />Encl. 2 copies <br />Cc: file CF 1.1.2.87 <br />Colowyo Coal Company, L.P. • 5731 State Highway 13 • Meeker, CO 81641 <br />T + 1 970 824 1578 • F +1 970 824 1598 • http://prospect.riotinto.org/iri/portal