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The total recoverable iron standard (1.0 mg/1) was exceeded nine times <br />this year. Excursions were normally related to high suspended solids. <br />The three NPDES site excu rsions occurred during snowmelt runoff in <br />April. This strict aquatic life standard was exceeded in 38% of the <br />premining stream samples. Three samples also exceeded the nitrite <br />standard. Nitrites are unst able in aerated water {Hem, 1989), and will <br />oxidize to nitrates. <br />Four samples from two sites exceeded the chronic selenium standard, 4.6 <br />ug/1. The acute standard, 18.4 ug/1, was not exceeded. <br />Six samples from five sites experienced exceedances of the sulfide <br />standard (0.002 mg/1 un-ionized) this year. Most excursions occurred <br />during snowmelt when suspended solid concentrations are high. The <br />analytical method available to SCC detects both dissolved sulfides and <br />acid-soluble metallic sulfides present in suspended matter. It is <br />suspected that a large portion of the sulfides detected is of the latter <br />type, which would bias the un-ionized results high. Any dissolved . <br />sulfides present in surface water should eventually oxidize to sulfates. <br />NPDES Effluent Criteria (Permit No. CO-0000221). Two excursions of <br />NPDES effluent criteria occurred this year. The excursions occurred at <br />Pond 014. A sample collected on April 12 had a TSS value of 170 mg/l. <br />The effluent limits are 35 mg/1 (monthly average) and 70 mg/1 (daily <br />max.). The same sample had a total iron value of 6.31 mgJl. The <br />effluent limits are 3 mg/1 (monthly average) and 6 mg/1 (daily max.). <br />The sample was collected during snowmelt runoff, and therefore, an <br />alternate of the TSS and total iron limits ("report") is allowed. The <br />settleable solids value was less than 0.4 ml/1. <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 />14 <br />