Laserfiche WebLink
<br />Only one of the iron excursions was at a NPDES site. NPDES4 experienced <br />this excursion in April. See the following NPDES Effluent section for <br />details. Only one of the nitrite excursions was at a NPDES site, NPDESB. <br />Nitrites will rapidly oxidize to nitrates. This excursion occurred in <br />April, when high flows in Fish Creek would have diluted this <br />concentration. <br />One sample (from NPDES4) had a selenium value that was less than an <br />elevated detection limit (5 ug/1 vs. a normal detection limit of 1 <br />ug/1), which was higher than the CDOH standard of 4.6 ug/1 (chronic). <br />The cause of this elevated detection limit was a decision by the <br />laboratory to dilute the samples prior to analyses in order to reduce <br />the effects of interferences (such as high salinity). <br />Five samples experienced exceedences of the sulfide standard (0.002 mg/1 <br />un-ionized) this year. The analytical method available to SCC detects <br />both dissolved sulfides and acid-soluble metallic sulfides present in <br />suspended matter. It is suspected that a large portion of the sulfides <br />detected is of the latter type, which would bias the un-ionized results <br />high. Any dissolved sulfides present in surface water should eventually <br />oxidize to sulfates. <br />In September 2003 (effective January 2004), the CDOH resegmented Grassy <br />Creek from Yampa Segment 12 to Segment 13e. Regulation 33 was further <br />revised in December 2005. Table 13 shows the new CDOH receiving stream <br />standards for Grassy Creek. Table 14 provides a comparison of those <br />standards to water quality data collected this year from NPDES and <br />stream sites in the Grassy Creek basin. Standards that were exceeded <br />are: <br />Parameter # of Sites / # of Excursions <br />Iron 2/3 <br />Mercury 1/1 <br />Sulfide 2/2 <br />• <br />r <br />J <br />22 <br />