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resulting from the occurrence of spoil springs after bacldilled spoil in <br />the mine pits has become saturated. Using conservative assumptions <br />regarding the amount of inflows to the reclaimed pits, and the quality <br />of spoil spring water, and information gathered from the neazby <br />Seneca II Mine in recent years, Seneca Coal Company has estimated <br />the changes in surface water quality which may be caused by the <br />pioposed Yoast Mine. The projected impacts on each of the affected <br />drainages near the permit area are summarized below. <br />Armand Draw <br />Following the occurrence of spoil springs at the Yoast Mine, the total <br />dissolved solid (TDS) content of surface water i^ Armand Draw is <br />projected to increase from 950 to 3938 mg/1. These values, and all <br />TDS values discussed below are mean TDS values during the irrigation <br />season, which was considered to last from June 1 through September <br />30. <br />No use is presently made of this water before it flows into Grassy <br />Creek. Due to the minimal flows in Armand Draw, it is reasonable to <br />assume that no future use of this water will be made, other than <br />livestock watering. Therefore, this increase in salinity will not result <br />in material damage. <br />Grassy Creek <br />An evaluation of the water quality impacts of the Yoast Mine on <br />Grassy Creek in the permit application projects no increase in TDS in <br />Grassy Creek downstream from the mine. This conclusion is drawn by <br />estimating the quality of Grassy Creek water after salt loading from <br />Yoast Mine spoil springs, and comparing that projected water quality <br />to current water quality in Grassy Creek downstream from the Yoast <br />permit area. Water in lower Grassy Creek currently has an average <br />TDS of 2584 mg/1, partially due to the influence of spoil spring <br />dischazges from the Seneca R Mine. Seneca Coal Company predicts <br />that lower Grassy Creek TDS will be 2177 mg/I after addition of Yoast <br />spoil springs. Thus, Seneca Coal Company concludes that TDS in <br />Grassy Creek will not increase as a result of Yoast Mine operations. <br />Using Seneca Coal Company's assumptions about spoil spring <br />development at the Yoast mine, and the existing baseline water quality <br />data for lower Grassy Creek, the Division estimated the TDS of lower <br />Grassy Creek after establishment of Yoast spoil springs will increase <br />by approximately five percent. Because the quantity and quality of <br />Grassy Creek water is marginal or unsuitable for use as domestic or <br />Yoast Mine 29 July G 1995 <br />