2012-06-20_PERMIT FILE - C2010089A (28)

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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 2 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 2 Park Lateral right -of -way. Down stream 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. The bottom and sides of the sediment pond will be compacted to a sufficient density to prevent leakage of pond water to the shallow bed rock zones. This method has been successful at the adjacent New Horizon Mine. 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. The post mining landscape is designed to protect the hydrologic balance by establishing slopes that generally will not exceed 5:1. Any highwall reductions will result in maximum slopes not to exceed 5:1. Reclaimed hillsides proposed for the New Horizon North mining area approximate the original pre- mining contours. Topsoil material will exhibit infiltration rates generally similar to pre- mining soils. At the NHN Mine, future reclaimed areas will be manipulated mechanically using chisel plowing and ripping of graded and top - soiled areas in combination with timely reseeding to minimize overland flow rates and volumes. Surface Water Monitoring WFC will continue to collect data from the baseline surface water monitoring sites (SW -N200 through SW -N209, minus SW -N206, destroyed by County maintenance) for the foreseeable future, (see Section 2.04.7 and Appendix 2.04.7 -2). It is anticipated that some of the sites may be relocated (with DRMS consultation) as mining Section 2.05.6(3) Page 6 November 2011