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Quantity of Surface Flows <br />The largest peak flow recorded in Annand Draw during baseline data collection <br />was 0.585 cfs. The presence of a sediment pond in Annand Draw will attenuate <br />peak flows in that drainage during mining. After mining, flows in Annand Draw <br />will increase due to establishment of spoil springs and additional runoff from the <br />reclaimed area. Spoil springs are projected to add approximately 0.073 cfs of base <br />flow to Annand Draw. <br />Spoil springs in Annand Draw and the Pond 11 drainage will add year-round base <br />flow to Grassy Creek. These spoil spring contributions are projected to increase <br />mean flows during irrigation season (June 1 -September 30) in Grassy Creek from <br />0.25 to 0.37 cubic feet per second downstream from the Yoast Mine. <br />Spoil springs are projected to add approximately 0. 159 cfs of base flow to Sage <br />Creek during irrigation season (June 1— September 30). These spoil spring <br />contributions are projected to increase mean flows during the irrigation season in <br />Sage Creek from 0.259 to 0.418 cfs. <br />Quality of Surface Water <br />The primary impact of Yoast mining operations on surface water quality will be an <br />increase in total dissolved solids concentration resulting from the occurrence of <br />spoil springs after backfilled spoil in the mine pits has become saturated. Using <br />conservative assumptions regarding the amount of inflows to the reclaimed pits, <br />and the quality of spoil spring water, and also using information gathered from the <br />nearby Seneca II Mine in recent years, Seneca Property, LLC has estimated the <br />changes in surface water quality which may be caused by the Yoast Mine. The <br />projected impacts on each of the affected drainages near the permit area are <br />summarized below. <br />Annand Draw <br />Following the occurrence of spoil springs at the Yoast Mine, the total dissolved <br />solids (TDS) content of surface water in Annand Draw is projected to increase <br />from 950 to 3938 mg/1. These values, and all TDS values discussed below, are <br />mean TDS values during the irrigation season, which is considered to last from <br />June 1 through September 30. <br />No use is presently made of this water before it flows into Grassy Creek. Due to <br />the minimal flows in Annand Draw, it is reasonable to assume that no future use of <br />this water will be made, other than livestock watering. Therefore, this increase in <br />salinity will not result in material damage. <br />24 <br />