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Creek basins. Standards that were exceeded (excluding ammonia and • <br />sulfide) are: <br />Parameter # of Sites / # of Excursions <br />Iron 2/2 <br />Mercury 1/1 <br />Nitrite 2/4 <br />The iron standard (1.0 mg/1) was exceeded two times this year. This <br />strict aquatic life standard was exceeded in 38~ of the premining stream <br />samples. Four samples also exceeded the nitrite standard. Nitrites are <br />unstable in aerated water (Hem, 1989), and will oxidize to nitrates. <br />One sample experienced a mercury value above the detection limit. This <br />value is thought to be in error since it an order of magnitude higher <br />than any other value previously observed at this site. Only 2 out of 42 <br />samples (since 1990) at this site (YSSF3, which is upstream of mining) <br />had values at the detection limit. • <br />In addition, one sample (from NPDESI2) had a chromium value that was <br />less than an elevated detection limit (20 ug/1 vs. a normal detection <br />limit of 10 ug/1), which was higher than the C-OH standards of 11 and 16 <br />ug/l. The cause of these elevated detection limits was a decision by the <br />laboratory to dilute the samples prior to analyses in order to reduce <br />the effects of interferences (primarily, high salinity). <br />Ammonia values require extra calculations to determine exceedences. The <br />standard is 0.06 mg/1 un-ionized NH3, while the method detects both un- <br />ionized NH3 and ionized NH4. The following table calculates the actual <br />un-ionized NH3 concentration of the exceedences reported on Table 12. <br />Ammonia values were calculated from the Internet site <br />http://aquanic.org/images/tools/ammonia.htm. <br /> <br />14 <br />