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20 Shoes [hat all surface eater sites, including NPDES sites, exhibited higher levels of select parameters than the standards established for Segment 13. Sulfate uas commonly higher than the stream standard at all sites in 1991. The sulfate standard of 250 mg/t is a reflection of a secondary drinking eater standard and is not a reflection of existing undisturbed eater quality as demonstrated at upstream (from mining) Sites 1 and 5. Other parameters that were analyzed at higher concentrations than the standards include sulfide (un-ionized), copper, lead, manganese, zinc, iron, and cadmium. Exceedences of the standards were present both at NPDES, upstream, and downstream sites. eater discharged from the Seneca II Mine is not used directly for irrigation. Indirectly, although, eater 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. 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. Nater discharged from the Seneca 11 Mine is used for livestock catering. Table 21 (Appendix A) presents the most stringent livestock siandards as compiled from various organizations by the OSMRE (OSMRE, 1989). Surface eater quality measured at stream and NPDES sites during the 1991 eater year were compared with the livestock standards, and the comparison results are presented in Table 22 (Appendix A). pH was measured at higher levels than the livestock standards, ranging from 8.53 at NPDES 008 to 8.98 also at NPDES 008. Aluminum was the only other parameter to exceed livestock standards. observed at Sites 11 and 13 in May, these high aluminum values may be attributed to high suspended solids (552 and 600 mg/l, respectively), or background conditions in the upgradient portions of the Fish Creek watershed. As a final note, only one exceedence of NPDES effluent criteria (Permit No. CO-0000221) was observed at the outfalls associated with the Seneca II Nine during 1991. On May 8, 1991 at NPDES 003, an oil/grease value of 214 mg/l was measured. No visible oil sheen uas noted, but oil appeared to be suspended ui thin The sample. This exceedence uas attributed to a truck wash settling pond that discharges into the NPDES 003 pond. This settling pond was dredged two weeks prior to the NPDES 003 oil/grease measurement. This dredging apparently re suspended oil and grease-laden sediment that later discharged into the NPDES 003 pond. Subsequent oil/grease analyses (range <1 mg/l detection limit to 2.0 mg/l) did not exceed the standard of 10.0 mg/l. 22