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The design of these structures can be found on Map F-I B. <br /> 9. Please provide narrative explaining ivIty the design proposed is adequate tvith respect <br /> ter flood mitigation requiremenis, <br /> The expanded mining area is entirely within the I 00-YR floodplain of the Yampa River, as is a <br /> great deal of the Bunn Ranch Pit. The priority is mitigating potential negative impacts to flood <br /> waters on and off the site. The primary potential source of negative impacts is potential "lake <br /> capture" leading to the Yampa River rerouting itself during a flood event. This can be prevented <br /> with appropriate protection of the be between the river and the eventual lake using <br /> inflow/outflow structures. <br /> The primary goal of an inflow/outflow structure is to prevent a large hydraulic head difference <br /> between the pit water level and the river water level during a flood. These structures facilitate the <br /> flow of water into and out of the pit without erosion of the pit side and river side banks during <br /> floods. Following floods, the river level will lower back below the bottom of these structures <br /> within its own channel. Therefore, preventing the river from rerouting itself via capturing of the <br /> lake. This prevention of"lake capture" is the goal of all flood protection measures for pits along <br /> the river at the Bunn Ranch Pit. Similar techniques have been used at an old pit immediately to <br /> the east within the permit area successfully. <br /> /0. It appears groundivater ivill be exposed in development of the requested expansion <br /> area, Ij'ground water ivill be exposed please provide DRUS with either of the,lb1loiving <br /> items prior to ewposing ground itater: <br /> a. A ivuler court augmentation plan <br /> b. Bonding estimation and monies to mitigate injurious stream depletions related <br /> to mining related exposure ofground ivater. This should include costs <br /> associated iviih backfilling of the pit to cover exposed ground water to a depth <br /> of nvojeet above the static ground ivaler level. <br /> c. Ij'a slurry wall or clay liner will be installed, the applicant must file and <br /> Antendinent application and receive DRUS approval of such a change. <br /> Currently the Yampa River basin in this area is under appropriated. Therefore, the only <br /> requirement for groundwater exposure is a current gravel well permit. See Item I for more <br /> discussion. <br /> Bunn Ranch TR 3 PUA <br />