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<br />Since the 100-year flood depth (3.26 feet) is expected to remain <br />below the level of excavation (five feet above the river thalweg <br />elevation, the Swan River will not be impacted by the removal of <br />the dredged tailings. If the flood exceeds the anticipated flood <br />elevations, the excavation of material will increase the conveyance <br />capacity of the river by providing some overbank area and thereby <br />reduce the flood elevations and velocities from historical <br />conditions. <br />r <br />The proposed operation is located in the river bed of the Swan <br />River. The river splits into two channels here and large piles of <br />mine and placer tailings were long ago placed between the two <br />channels. This operation will be removing the tailing piles from <br />the river channel, but will not expose groundwater as the average <br />original ground level is approximately five feet above the river <br />thalweg elevation. <br />Figure G-1 shows the location of all permitted and decreed <br />groundwater wells in the area within a 1,000 feet radius of the <br />property. Since no dewatering or exposure of the groundwater will <br />occur, these wells will not be impacted. <br />Water Rights <br />No water rights are associated with this property or needed for <br />this operation. <br />Wash Water <br />There will be no consumptive use of water at this site. The <br />cobbles are dry in their natural location above the normal river <br />elevation, therefore, no water adheres to the material removed from <br />the site. The operation will not include washing so no process <br />water is generated or consumed. Since no ponds will be constructed <br />for treating process water, no groundwater will be exposed. <br />Dust Control <br />Since County Road 6 is paved and the roads that will be used for <br />access onto the property are of such coarse aggregate, there is no <br />anticipated need for watering to control dust. <br />Stormwater Runoff <br />The majority of contaminants that occur from a sand and gravel mine <br />are either sediment, oil, or grease. The proposed mining operation <br />will use the following measures to protect the area from pollution <br />due to stormwater runoff. <br />G-2 <br />