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The Colorado Water Quality Control Commission (CWQCC) has established segment <br /> specific aquatic life water quality standards (CDPHE, Reg. 33) for upper Dry Creek <br /> (Yampa River Segment 13d) and Sage Creek (Yampa River Segment 13e). Therefore, <br /> the following surface water quality discussion has been organized by drainage basin. <br /> The 2020 Water Year surface water quality data is provided in Appendix D. Samples <br /> from this year's stream points are compared to both the Colorado Department of <br /> Public Health 6t Environment (CDPHE) surface water agricultural use standards <br /> (CDPHE, Reg. 31) and the appropriate segment specific aquatic life water quality <br /> standards. Samples from NPDES outfalls are compared to NPDES discharge limits as <br /> well as the segment specific aquatic life standards. Additional discussion of the water <br /> quality in each stream segment follows. <br /> 4.1 DRY CREEK <br /> Analytical results for the 2020 surface water monitoring conducted at the four Dry <br /> Creek stream points is provided in Table D.1 of Appendix D and the results of the Dry <br /> Creek outfalls are included in Tables D.2 through D.S. There were no exceedances of <br /> any NPDES permit limit or Yampa Segment 13d water quality standard at the four Dry <br /> Creek NPDES Outfalls in 2020. The stream points were compliant with all Agricultural <br /> Use standards and all Yampa Segment 13d standards except for total recoverable <br /> iron, sulfide, and mercury. <br /> Total recoverable iron exceeded the Yampa Segment 13d surface water quality <br /> standard twice at steam point WSH7 and three times at WSHF1. Table D.6 provides a <br /> statistical summary of the pre-mine total recoverable iron measured at Dry Creek <br /> stream points WSH7, WSHF1, and WSDS. None of the total recoverable iron <br /> exceedances in 2020 were outside of the range measured prior to mining. <br /> Synoptic watershed monitoring was conducted at the Dry Creek outfalls and stream <br /> points on April 22nd, July 21st, and September 1st. Exceedances of the iron standard <br /> occurred at stream points WSH7 and WSHF1 during the July 21st and September 1st <br /> events. However, no exceedances of iron occurred at Outfalls 006, 016, and 017 <br /> during these events and the iron concentrations at the outfalls were an order of <br /> Page 11 of 17 <br />