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The total surface disturbance on North Thompson Creek is 52 acres (reference <br />• sheet 3 and figure 1, Appendix 4-B, Final Design Calculations; areas 8, 11, 12, <br />13A, and 13B), which is 0.2 percent of the entire watershed area, The total <br />acreage passing through drainage structures (ditches, ponds, and culverts) is <br />350 acres (areas 3 through 13, sheet 3 of Appendix 4-B), which is 1.4 percent of <br />the entire watershed drainage area. Using state-of-the-art surface runoff <br />models such as the SCS unit hydrograph method or the technique described in the <br />Bureau of Reclamation publication, Design of Small Dams, the pre- and post- <br />mining hydrographs would not be perceptibly different. This fact, along with <br />the assumptions inherent in the selection of runoff curve numbers for surface <br />cover conditions, would make any attempts to definitively quantify the effects <br />of mining or North Thompson Creek flow rates a meaningless exercise. Likewise, <br />the effects of final reclamation on such a relatively minor portion of the <br />watershed would he imperceptible. <br />There has been no detectable change in runoff or flow characteristics on Plorth <br />Thompson Creek due to the construction of surface facilities at the mine, The <br />surface facilities have been built in areas that would not obstruct surface <br />• runoff or drainage to the stream. When the increase in runoff from the facili- <br />ties is compared to the runoff of the total drainage area of the watershed, the <br />increase is insignificant. <br />Recharge capacity of the mine area has not been affected by surface disturban- <br />ces. The surface area disturbance is very small when compared to the total area <br />of recharge. Any water that is displaced by surface disturbance travels a short <br />distance before reaching a recharge area. <br />Infiltration and evapotranspiration rates will be altered upon final reclamation <br />of the disturbed acreage. Importing topsoils for final reclamation will result <br />in a final reclaimed soil profile that would allow more tnfiltration than the <br />original, undisturbed shallow soils. However, the effects of the altered <br />infiltration and evapotranspiration rates on the entire watershed's flow rates <br />would be imperceptible due to the minor percentage of watershed area involved, <br />• <br />4-110 <br />