2016-01-07_PERMIT FILE - C2010089A (11)

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Those areas that are affected by mining will be graded to post mining topographies that generally feature slopes no greater than 5:1. In combination with the reclamation and topsoil handling techniques, reduced slopes will minimize the potential for erosion due to accelerated sheet wash or gullying. Diversions will be designed according to accepted design criteria, and will be built to minimize erosion and prevent additional contributions of sediment by limiting the flow velocities and tractive forces that cause erosion. Temporary diversions in place longer than a growing season will be seeded with a temporary seed mix as outlined in Section 2.05.4(2)(e). Diversions have been designed to maximize geomorphic stability while minimizing disturbance. All temporary diversions will be removed and reclaimed after mining activities have been completed. Plans have been developed for water rights augmentation pumping that will meet effluent limitations and minimize erosion. Drainage from haulage and access roads will be routed to the sediment pond. Where necessary, culverts will be designed and constructed using approved engineering design criteria to minimize erosion and prevent the contribution of additional sediment to runoff. Surface Water Quantity The Operations Plan - New Horizon North (Map 2.05.3-1) details pond diversion and culvert locations that will control all drainage into, through and out of New Horizon North mining area. Surface water flow at NHN is primarily the product of seasonal irrigation, (See Section 2.04.7). The 2nd Park Lateral will be diverted through a HDPE pipeline around the mining area. Once mining has advanced far enough to the north, the HDPE pipeline will be moved to the approximate original 2nd Park Lateral right-of-way. Downstream irrigation water flow will not be interrupted. The plan has been developed for insuring that changes in surface water quantities are minimized. The impact of designed structures proposed for the New Horizon North mining area (sediment pond, diversion ditches, culverts, etc.), was determined to have no significant effect on surface water quantity (see Probable Hydrologic Consequences at the end of this section). The sediment ponds have been designed according to acceptable engineering criteria to contain (at a minimum) the 10 -year, 24-hour runoff volumes. WFC will ensure that the ponds maintain this capacity by dewatering and/or excavating excessive sediment accumulated according to plans outlined in Section 2.05.3(3), Mine Facilities. Diversions have been designed to pass the 10 -year, 24-hour runoff volumes in accordance with approved engineering design criteria. Culverts and road drainage -ways will insure that runoff originating within or outside each mining area will be controlled and adequately routed through to minimize changes in surface water quantities. Section 2.05.6(3) Page 6 Sept. 2015 (TR -11)