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NUVEMCO LAST CHANCE MINE <br />STORM WATER MANAGEMENT PLAN <br />Mine Portal and Temporary Ore Stockpile <br />Run -on is prevented from this area through a combination of natural topography and <br />earthen berms as shown on Figure 1. The ore area is very flat. An earthen berm <br />beginning at the north side of the topsoil stock pile and running generally to the west will <br />prevent run -on from entering the area and storm water from leaving the area and protect <br />the slopes. The haulage road will be graded to drain into the hill on the east side to <br />prevent runoff from leaving the study area and divert it into the mine portal. The <br />northwest side of the haulage road will also have an earthen berm to divert runoff into the <br />mine portal. All of the runoff generated from this study area, including storm water that <br />contacted the ore, will be diverted into the mine portal. The study area is 0.46 acres in <br />area. The runoff from this area was not computed. <br />Sediment Pond #1 <br />This area comprises the largest area. This area is 1.08 acres in size and includes the <br />waste rock dump, trailer, and parking. An earthen berm will be constructed on the <br />southwest and northwest sides of the area to direct flows into Sediment Pond #1. This <br />area is adjacent to the Mine Portal and Temporary Ore Stockpile area described above. <br />All of the storm water generated from this area will flow to Sediment Pond #1, located in <br />the north end of the study area. Approximately 25% of this area is undisturbed. This <br />area will be used to expand the waste rock dump and will be considered disturbed in the <br />run -off calculations. <br />Sediment Pond #2 <br />The study area is 0.18 acres. It is separated from the Mine Portal and Temporary Ore <br />Stockpile area by an earthen berm. A topographic high separates this area from the <br />Sediment Pond #1 area. Some run -on occurs from the small hill to the southwest which <br />is vegetated with sage brush, juniper and native grasses. The remainder of the area is <br />bare earth. All of the storm water generated from this area will flow into Sediment Pond <br />#2. <br />The total area for all three basins described above is 1.72 acres. Photographs of the study <br />area are included in Appendix A. <br />PEAK RUNOFF <br />There are several methods that can be used to compute the peak runoff from the area. <br />The size of the area is such that many of the methods are not suitable for such a small <br />area. The Rational Method is suitable for areas up to 140 — 160 acres. The Rational <br />Method was selected where: <br />Q =CiA <br />Q = peak discharge cubic feet per second (cfs), <br />C = Rational Method runoff coefficient <br />March 2010 2 <br />