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Surface Water Summary <br />The Yoast Mine PHC (PAP Tab 17, Attachment 17-5) predicts TDS increases <br />to be observed at various stream sites during the irrigation season <br />(June-September). The following table outlines those predictions along <br />with this year's observed averages. This table indicates that no TDS <br />predictions were exceeded this year. <br />Stream Site Predicted TDS values (mg/1) This years average TDS (mg/1) <br />YSGFS 1337 945 <br />NPDESIO 3938 2050 <br />NPDESI2 4291 2960 <br />WSSF3 (Seneca II-W site) 2118 835 <br />TDS trends are increasing at all NPDES and downstream stream sites. <br />Water discharged from the Yoast Mine is not used directly for <br />irrigation. Indirectly, although, water discharged from the mine is <br />significantly diluted by water from Grassy Creek, Sage Creek, or the <br />Yampa River before it is diverted and used for irrigation. Due to the <br />relative amount of dilution, the ambient water qualities of Grassy <br />Creek, Sage Creek, and the Yampa River are the dominant factors in <br />determining their suitability for irrigation. Water discharged from the <br />Yoast Mine is, however, used for livestock watering. <br />References <br />American Public Health Association (Ed.). 1985. "Standard Methods for <br />the Examination of Water and Wastewater", 16th Edition, Washington, <br />D.C. <br />Brakensieh and others. 1979. "Field Manual for Research in Agricultural <br />Hydrology". <br />Buchanan and Sumers. 1968. "Stage Measurements at Gaging Stations". <br /> <br />16 <br />