2022-12-19_GENERAL DOCUMENTS - C1981010

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Colorado, and Yampa Rivers should be placed on the 303(d) list of state impaired waters due to these high mercury concentrations found in fish tissue. To summarize, Colorado pikeminnow have repeatedly shown elevated mercury concentrations in both the Yampa and White Rivers. Some of the mercury concentrations measured in pikeminnow from the White River have been especially high. After reviewing several studies on mercury toxicity in fish, it is reasonable to assume that some individual Colorado pikeminnow are being adversely affected by elevated mercury tissue residues. However, we do not know what level of impact mercury has had on the Colorado pikeminnow at the population level in the action area in the past. We do not know if it is limiting or preventing successful reproduction, particularly in the White River where mercury levels are higher and reproduction rates are low. Although likely to be lower than Colorado pikeminnow, due in large part, to trophic position, mercury levels have not been tested in the other three endangered fish species. 3.3.2 Selenium During surface water sampling of the Yampa River between 1997 and 1998, selenium concentrations ranged from; <1 to 4.8 µg/L near Craig, CO< 1 to 4.9 µg/L near Maybell, CO and<1 to 3.6 µg/L near Deerlodge Park, CO (USGS 2001). The peak reported selenium concentrations for these sites occurred in March, possibly during the beginning of the snow runoff. Concentrations were <1 µg/L during May through October. A longer term data set from 1991 to 2011 for the Yampa River below Craig Colorado (USGS Station 09247600) (n=91), showed that close to half of the sample values were reported at less than the laboratory reporting level (0.030 µg/L), and the maximum reported selenium concentration was 17.0 µg/L (USGS 2015). The chronic aquatic life standard for selenium is 5 µg/L total and 4.6 ug/L dissolved (CDPHE 2012a). In sum,historic selenium concentrations measured in the Yampa River below Craig have exceeded the chronic aquatic life selenium standard approximately 10 percent of the time, but are generally below the standard, and this segment is not state listed under 303(d) of the Clean Water Act as impaired for selenium (CDPHE 2012b; USGS 2015). According to USGS (2015)water sampling in the White River beginning in the 1990s, water selenium concentrations have always remained below the chronic aquatic life standard both above and below Taylor Draw Dam. Because selenium bioaccumulates in aquatic food chains, selenium concentrations in fish tissue, rather than water,provide a better indication of potential adverse impacts. The available data is limited,but a few studies have provided selenium concentrations measured in fish tissue samples collected from the Yampa and White Rivers. Osmundson and Lusk(2012)reported on selenium in muscle plug samples taken from archival Colorado pikeminnow collected from the Yampa River during 1962-1966, which averaged 7.5 µg/g DW (5.9-10.1 ug/g DW). According to Lemly (1995,p.281), these fish would be ranked into the "High"hazard category (after conversion of whole body to egg concentrations), which "denotes an imminent,persistent toxic threat sufficient to cause complete reproductive failure in most species of fish and aquatic birds." Selenium concentrations in muscle plugs taken from five Colorado pikeminnow collected from the Yampa River during 1996 ranged from 1.7-2.8 µg/g DW (mean of 2.3 ug/g DW) (Hamilton et al. 2004) which places them in the "Minimal"hazard category (Lemly 1995). The Minimal hazard 40