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NPDES Effluent Criteria (Permit No. CO -0000221 <br />No excursions of NPDES limits occurred this year. <br />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. <br />Stream Site Predicted TDS values (mg/1) This year's average TDS (mg/1) <br />YSGF5 1337 990 <br />NPDES10 3938 2325 <br />NPDESI2 4291 3026 <br />WSSF3 (Seneca II -W site) 2118 1060 <br />No sites exceeded the PHC predictions. <br />TDS trends are increasing at NPDESI0, NPDESII, NPDESI3, NPDESI4; Stream <br />Sites YSS2, YSGF5 and YSGS; and Spoil Spring 3 (YSSPG3). TDS values have <br />decreased at NPDESI2, YSSF3 and Spoil Springs 1 (YSSPGI), and 2 <br />(YSSPG2). A recently stable trend has been observed at Spoil Spring 4 <br />(YSSPG4). Average flow values this year were below historic averages at <br />all NPDES sites, except NPDESI2. <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 />16 <br />