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Response to Exhibit C, Comment 3 <br />The gravel soil throughout the river bottom is so <br />permeable that there is no surface runoff from natural <br />precipitation events either into, through, or out of the mining <br />area. Therefore, the only surface water to be dealt with is that <br />flowing in the Uncompahgre River. <br />Several gravel dikes have been constructed within the <br />river's floodplain between Ouray and Ridgway to control <br />flooding. The existing berm shown on Exhibit E is such a dike. <br />It has been in place for a long period of time, was shown on the <br />Floodplain Study Maps prepared for the Colorado Wat is 'tbi17` <br />Conservation Board in 1978, and has withstood e record high <br />flows that occurred during the spring of 1983. This berm is <br />considered stable and will be used as is to separate the Phase I <br />and Phase II operations. <br />The proposed mining operation includes construction of <br />a diversion dike to shift the active channel into the Phase I pit <br />during Phase II mining and extension of the existing berm to <br />prevent backflow from the Phase I pit into the Phase II pit. <br />These dikes will be constructed of the same materials and in the ~y <br />same manner as the existing berm. ,,,,~~` fir-! ~~-e G-,---~~+^; ~-- ~t <br />tt,.t eu,sf;~-, G.~-r-.-~- <br />It is not the intent of the mining plan to protect the <br />operation during a 100-year flood event. To do so would <br />necessitate construction of large, heavily reinforced dikes that <br />would impede flood flows and reduce the floodplain area. This <br />could result in severe impacts to adjacent properties. The <br />mining plan instead is to leave the pit area unprotected as much <br />as possible so that flood events will be unimpeded. The only <br />protection to be offered will be in the form of a sill to be <br />constructed in the riverbed at the upstream end of the pits and <br />two small areas of riprap reinforced banks. The sill will <br />prevent down-cutting by the river as its flow enters the mined <br />area, thus protecting upstream land owners. The reinforced banks <br />will prevent lateral erosion from occurring where the mine <br />diversions cause a change in flow direction. <br />Page 2 <br />