2009-02-26_REPORT - C1980005 (7)

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Discharge Monitoring Reports, dated October 21, 2008 to the CDPHE. A copy was also provided to the CDRMS. Surface Water Summary. Water discharged from the Seneca II Mine is not used directly for irrigation. Indirectly, although, water discharged from the mine is significantly diluted by water from either Fish Creek or the Yampa River before it is diverted and used for irrigation. No irrigation exists on Grassy Creek below Seneca II. Due to the relative amount of dilution by additional water from both sources, the ambient water qualities of Fish Creek and the Yampa River are the dominant factors in determining their suitability for irrigation. Water discharged from the Seneca II Mine is, however, used for livestock watering. TDS values at NPDES 002 are increasing at a moderate rate while values at NPDES 003 are decreasing. TDS values at NPDES 004 and 008 appear to be stabilizing. On lower Grassy Creek (SSG2), TDS values are increasing. Of the ten spoil springs monitored, two exhibit an increasing EC trend, six are exhibiting decreasing EC trends, while two display a stable EC trend. NPDES discharges are normally suitable for livestock and irrigation, but sometimes exceed water quality standards for aquatic life. A 76 mg/1 increase in TDS was predicted by the PHC for Fish Creek in June, while a 20 mg/1 increase was observed at Site SSF13. In July, a 74 mg/l increase was predicted, while a 40 mg/l decrease was observed. TDS values at lower Grassy Creek (SSG2) were above predicted values. The winter snowpack for this year was above average, but only one of the four NPDES sites exhibited annual average flows above the historic averages. The timing of when the monthly flow values were determined account for the below average flow values at the remaining NPDES sites. American Public Health Association (Ed.). 1985. "Standard Methods for • the Examination of Water and Wastewater", 16th Edition, Washington, D.C. 21