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SCC chooses to use those ground water use standards classifications <br />(livestock or irrigation) for surface water use evaluation. <br />Parameter # of Sites / # of Excursions <br />Manganese (CDPHE irrigation) 3/4 <br />This summary indicates that only one CDPHE surface water agricultural <br />use standards were exceeded. The manganese standard was exceeded at <br />three sites. However, as indicated in the recently revised CDPHE <br />Regulation 31, the standard of 0.2 mg /1, applies to plants grown in <br />acidic (<6.0 pH) soils. In alkaline soils, as are found in the PSCM <br />region, a more appropriate (EPA) standard would be 10• mg /1. All sites <br />had manganese values less than 1 mg /l. It should also be noted that the <br />site on Grassy Creek (SSG1) that is upstream of PSCM and Seneca II <br />discharges has often experienced exceedances of the 0.2 mg /1 standard. <br />Table 12 shows the CDPHE receiving stream standards for Fish Creek <br />(Yampa Segment 13b). Table 13 provides a comparison of those standards <br />to water quality data collected this year from NPDES4 and Site SSC10 (no <br />flow at SSC10 in June of July) in the Fish Creek basin. The stream <br />standards for Fish Creek are based on aquatic life standards, even <br />though there are no fish present in the upper portion of the tributary <br />that NPDES4 discharge into. Standards that were exceeded are: <br />Parameter # of Sites / # of Excursions <br />Selenium 1/2 <br />Two samples from NPDES4 exceeded the chronic selenium standard, 4.6 <br />ug /l, in March and June, with values of 6.5 and 5.7 ugh', respectively. <br />The acute standard, 18.4 ug /1, was not exceeded. See the following NPDES <br />effluent section for more details. <br />In September 2003, the CDPHE resegmented Grassy Creek from Yampa Segment <br />12 to Segment 13e. Regulation 33 was further revised in December 2005 <br />and August 2008. Table 14 shows the new CDPHE receiving stream standards <br />for Grassy Creek. Table 15 provides a comparison of those standards to <br />17 <br />