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• water use evaluation. Following is a list of standards exceeded this <br />year. <br />Parameter # of Sites / # of Excursions <br />Manganese (CDOH, SW, irrigation) 2/3 <br />Review of this list indicates that only one CDOH surface water <br />agricultural use standards was exceeded. The manganese standard was <br />exceeded at two sites. However, as noted previously in the ground water <br />discussion, the relatively low CDOH standard of 0.2 mg/1, according to <br />the EPA, applies to plants grown in acidic soils. In alkaline soils, as <br />are found in the Yoast region, a more appropriate (EPA) standard would <br />be 10 mg/1. The maximum manganese value for any surface water site <br />observed this year was 0.34 mg/1. Premining manganese values often <br />exceeded the 0.2 mg/1 standard. <br /> Table 11 shows the CDOH receiving stream standards for Sage Creek (Yampa <br />• Segment 13d). Table 12 provides a comparison of those standards to water <br /> quality data collected this year from NPDES and stream sites in the Sage <br /> Creek basin. Standards that were exceeded (excluding ammonia and <br /> sulfide) are: <br />Parameter # of Sites / # of Excursions <br />Nitrite 2/5 <br />Selenium 1/i <br />Nitrites are unstable in aerated water (Hem, 1989), and will oxidize to <br />nitrates. The one selenium value exceeded the chronic (30 day average) <br />standard but not the acute (one day max.) standard. <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 />13 <br />