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• NPDES Effluent Criteria (Permit No. CO-0000221). Two excursions of <br /> NPDES effluent criteria occurred thi s year. On October 11, 2001, a <br /> sample from NPDE512 had a TSS value of 60 mg/1 (limit 35 mg/1). However, <br /> since the sampling occurred within 4 8 hours of a 0,88 inch rainfall <br /> event, this TSS value is allowable (rainfall exemption) . The second <br /> excursion occurred on August 13, 2002, when a sample from NPDESI0 had a <br /> TSS value of 46 mg/1 (limit 35 mg/1). This discharge was the result of <br /> siphoning the pond prior to dredging. Now that the pond is cleaned out, <br /> no further excursions should occur. <br />• <br />• <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. This table indicates that no TDS <br />predictions were exceeded this year. <br />Stream Site Predicted TDS values <br />YSGFS 1337 <br />NPDESIO 3938 <br />NPDESI2 4291 <br />WSSF3 (Seneca II-W site) 2118 <br />1) This years average TDS (mg/I) <br />970 <br />3280 <br />1868 <br />700 <br />TDS trends are increasing at all NPDES and stream sites. Water <br />discharged from the Yoast Mine is not used directly for irrigation. <br />Indirectly, although, water discharged from the mine is significantly <br />diluted by water from Grassy Creek,' Sage Creek, or the Yampa River <br />before it is diverted and used for irrigation. Due to the relative <br />amount of dilution, the ambient water qualities of Grassy Creek, Sage <br />Creek, and the Yampa River are the dominant factors in determining their <br />suitability for irrigation. Water discharged from the Yoast Mine is, <br />however, used for livestock watering. <br />IS <br />